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FPInnovations
319 Franquet Street
Québec, Québec G1P 4R4
Transformative Technologies Program
Project TT5.15
No. 201002167
Hardwood Initiative—Element 5: Development of new
processes and technologies in the hardwood industry
Coloring and Decolorizing Wood via Biotechnology
by
Dian-Qing Yang and Manon Gignac
Research Scientist
Lumber Manufacturing Department
March 2011
Dian-Qing Yang
Project Leader
Manon Gignac
Reviewer
Francis Fournier
Department Manager
© 2011 FPInnovations. All rights reserved.
This published Work is designed to provide accurate, authoritative information but it is not intended to provide professional
advice. If such advice is sought, then services of a FPInnovations professional could be retained.
Abstract
Wood color has an important economical impact on wood products. The hardwood lumber industry is
facing a particular increase in demand by their customers for wood with an attractive, consistent and
specified color. Fungi are a specific group of micro-organisms that can affect wood color. Some fungal
species produce various colorful pigments during their growth and can create a preferable color or pattern
on wood products, whereas some other species produce bleaching enzymes that can clean unpleasant
stained wood products. The objectives of this project were to increase the average value of the hardwood
lumber product mix by developing a biological technology to eliminate undesirable wood colors and to
produce attractive and consistent wood colors and patterns.
Thirty-five fungal species were selected for coloring wood of sugar maple, white birch and yellow birch,
whereas 20 fungal species were selected for decolorizing stained wood (chemical or biological stains) of
sugar maple, yellow birch and white pine. The wood samples were dip-treated for 30 seconds in spore
suspensions and incubated at 25°C and 75% RH up to 8 weeks. Wood color changes were visually
inspected weekly and final colors were measured with a colorimeter.
The results of coloring wood show that 15 fungal species are promising to color wood of sugar maple,
white birch and yellow birch into red, brown, green, grey, black and purple. The heartwood was equally
colored as sapwood with most fungal species. Application of 3 or more selected fungal species together
on a piece of wood was able to produce a rainbow wood pattern with multiple colors. The process for
coloring wood required 1-4 weeks. Weathering gradually reduced color intensity of biologically stained
wood if without a protective coat.
The results of decolorizing wood show that 17 fungal species are promising: 10 fungal species were able
to decolorize white pine blue stain, 3 species decolorize white pine coffee stain, 10 species decolorize
sugar maple stains and 11 species decolorize yellow birch stains. Based on visual and instrumental
evaluation for color brightness and uniformity of decolorized wood samples, 3 fungal species were
identified as potential candidates for decolorizing white pine blue stain, 1 species for white pine coffee
stain, 4 species for sugar maple stains and 4 species for yellow birch stains. The process for decolorizing
wood required 2-8 weeks.
iii
Table of contents
Abstract ......................................................................................................................................................................... iii
List of Tables.................................................................................................................................................................. v
List of Figures ................................................................................................................................................................ v
1 Objectives ...............................................................................................................................................................1
2
3
Introduction .............................................................................................................................................................1
Background .............................................................................................................................................................2
4
5
Staff ........................................................................................................................................................................3
Materials and Methods............................................................................................................................................3
5.1
Coloring wood with fungi ..............................................................................................................................3
5.1.1 Selection of fungal species for coloring ....................................................................................................3
5.1.2 Preparation of fungal solutions and wood specimens for coloring ...........................................................4
5.1.3 Treatment of wood specimens and evaluation .........................................................................................6
5.1.4 Effects of treatment conditions on wood coloring quality..........................................................................7
5.1.5 Production of multiple colors on wood ......................................................................................................8
5.2
Decolorizing wood stain with fungi................................................................................................................9
5.2.1 Preparation of fungal materials ................................................................................................................9
5.2.2 Preparation of wood specimens for treatment ........................................................................................10
5.2.3 Treatment of wood specimens and evaluation .......................................................................................11
6
Results ..................................................................................................................................................................12
6.1
Coloring wood with pigmented fungal species............................................................................................12
6.1.1 Wood coloring with selected fungal species ...........................................................................................12
6.1.2 Color variations on sapwood and heartwood of three treated wood species .........................................18
6.1.3 Color uniformity and penetration into wood ............................................................................................24
6.1.4 Color resistance to weathering ...............................................................................................................27
6.1.5 Effects of treatment conditions on wood coloring quality........................................................................31
6.1.6 Production of multiple wood colors by the treatment ..............................................................................36
6.2
Decolorizing wood stain with bleaching fungal species ..............................................................................41
7
8
Discussion.............................................................................................................................................................49
Conclusions ..........................................................................................................................................................49
9
Recommendations ................................................................................................................................................50
10 References............................................................................................................................................................50
iv
List of Tables
Table 1
Table 2
Table 3
Table 4
Table 5
Table 6
Table 7
Table 8
Table 9
Table 10
Table 11
Table 12
Table 13
Table 14
Table 15
Table 16
Selected fungal species from agar plate test ............................................................................................3
Fungal species used for coloring wood at different treatment conditions .................................................8
Fungal species used for producing multiple colors on wood ....................................................................9
Selected fungal species for decolorizing wood stains.............................................................................10
Fungal coloring on wood specimens ......................................................................................................14
Wood color change (ΔE*) after fungal treatment and drying ..................................................................19
Fungal color uniformity and penetration into wood .................................................................................25
Fungal coloring of sugar maple wood in different treatment conditions ..................................................32
Fungal coloring of nwhite birch wood in different treatment conditions ..................................................33
Fungal coloring of yellow birch wood in different treatment conditions ...................................................34
Fungal color penetration into wood in different treatment conditions......................................................35
Summary of fungal color penetration into wood in different treatment conditions...................................36
Multiple colors on wood by fungal treatment ..........................................................................................37
Fungal species with capacity of decolorizing wood stains ......................................................................42
Decolorization of wood stains by various fungi .......................................................................................43
Most promising fungi for decolorizing wood stains by visual evaluation .................................................44
List of Figures
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
Figure 10
Figure 11
Figure 12
Figure 13
Figure 14
Figure 15
Figure 16
Agar cultures of fungi used for wood coloring test ....................................................................................4
Transferring agar cultures to liquid cultures for wood coloring test...........................................................5
Fungal liquid cultures for wood coloring test .............................................................................................6
Treatment of wood samples with fungal liquid cultures for coloring..........................................................7
Blue stain (top) and coffee stain (bottom) of white pine samples used in the test ..................................11
Internal stain and end stain wood samples of sugar maple (top) and yellow birch (bottom) used
in the test ................................................................................................................................................11
Treatment of wood samples with fungal liquid cultures for decolorizing unpleasant wood color ............12
Coloration of wood samples with fungi ...................................................................................................15
Fungal coloration (red) on heartwood and sapwood of sugar maple ......................................................16
Color changes of wood samples caused by fungus Poria aurea ............................................................16
Spot wood pattern produced by fungus Trogia crispa ............................................................................17
Spalted wood pattern produced by fungus Polyporus dryophilus var. vulpinus ......................................17
Red color changes of wood samples dried at different temperatures .....................................................18
Brown wood color variation between sapwood and heartwood caused by Trogia crispa (473C) ...........20
Grey wood color variation between sapwood and heartwood caused by Penicillium
expansum (828A) ...................................................................................................................................20
Visual appearance of black coloration of sugar maple sapwood (left) and heartwood (right) caused
by Aureobasidium pullulans ....................................................................................................................21
v
Figure 17
Figure 18
Figure 19
Figure 20
Figure 21
Figure 22
Figure 23
Figure 24
Figure 25
Figure 26
Figure 27
Figure 28
Figure 29
Figure 30
Figure 31
Figure 32
Figure 33
Figure 34
Figure 35
Figure 36
Figure 37
Figure 38
Figure 39
Figure 40
Figure 41
Figure 42
Figure 43
Figure 44
Figure 45
Figure 46
Figure 47
Figure 48
Black wood color variation between sapwood and heartwood caused by
Aureobasidium pullulans (132I) ..............................................................................................................21
Visual appearance of purple coloration of yellow birch sapwood (left) and heartwood (right)
caused by Dactylium dendroides ............................................................................................................22
Purple wood color variation between sapwood and heartwood caused by Dactylium
dendroides (597A) ..................................................................................................................................22
Visual appearance of red coloration of white birch sapwood (left) and heartwood
(right) caused by Arthrographis cuboidea ...............................................................................................23
Red wood color variation between sapwood and heartwood caused by
Arthrographis cuboidea (706B) ...............................................................................................................23
Visual appearance of green coloration of sugar maple sapwood (left) and heartwood (right)
caused by Chlorosplenium aeruginascens .............................................................................................24
Green wood color variation between sapwood and heartwood caused by
Chlorosplenium aeruginascens (401A)...................................................................................................24
Uniformity of wood samples stained with A. cuboidea (red) and C. aeruginascens (green) ..................26
Penetration of red color into wood stained by A. cuboidea .....................................................................26
Color changes of untreated wood samples at different weathering times...............................................27
Black color changes of wood samples treated with fungal strain 132I at different weathering times .....28
Green color changes of wood samples treated with fungal strain 401A at different weathering times ...28
Purple color changes of wood samples treated with fungal strain 597A at different weathering times ...29
Red color changes of wood samples treated with fungal strain 110A at different weathering times ......29
Light brown color changes of wood samples treated with fungal strain 754A at different
weathering times ....................................................................................................................................30
Brown color changes of wood samples treated with fungal strain 31A at different weathering times .....30
Grey color changes of wood samples treated with fungal strain 828A at different weathering times .....31
Multiple colors produced by the fungal species 401A + 706B + 597A ....................................................37
Multiple colors also produced by the fungal species 401A + 706B + 597A ............................................38
Multiple colors produced by the fungal species 387AN + 706B + 597A .................................................38
Multiple colors produced by the fungal species 483A + 706B + 597A ....................................................39
Multiple colors produced by 8 fungal species .........................................................................................39
Rainbow wood pattern produced by a joint treatment with fungal species 483A + 706B + 597A ..........40
Rainbow wood pattern produced by a joint treatment with fungal species 387AN + 706B + 597A .......40
Rainbow wood pattern produced by a joint treatment with fungal species 401A + 706B + 597A ..........40
Rainbow wood pattern produced also by a joint treatment with fungal species 401A + 706B + 597A ..41
Rainbow wood pattern produced by a joint treatment with 8 fungal species ..........................................41
Decolorization of white pine blue stain by various fungi .........................................................................44
Decolorization of white pine coffee stain by various fungi ......................................................................45
Decolorization of sugar maple stains by various fungi ............................................................................45
Decolorization of yellow birch stains by various fungi .............................................................................46
Decolorized (lower part) blue stain and coffee stain on white pine wood samples by Trogia crispa
(473C, left) and Phlebia radiata (345A, right), respectively ....................................................................46
vi
Figure 49
Figure 50
Figure 51
Figure 52
Decolorized (lower part) sugar maple stains by Bjerkandera adusta (75A, left) and Trogia crispa
(473C, right), respectively .......................................................................................................................47
Decolorized (lower part) yellow birch stains by Merulius tremellosus (52A, left), Phanerochaete
chrysosporium (284A, middle) and Pleurotus ostreatus (71A, right), respectively.................................47
Uniformly decolorized sugar maple stained wood samples by the fungus Bjerkandera
adusta (75A) ...........................................................................................................................................48
Non-uniformly decolorized sugar maple stained wood samples by the fungus Phlebia
radiata (345A) .........................................................................................................................................48
vii
1
Objectives
This project is part of a research initiative designed to enhance the competitiveness of the hardwood
industry in eastern Canada. Project funding was provided by Natural Resources Canada's Transformative
Technologies Program and Québec’s Ministère des Resssources naturelles et de la Faune industrial
development strategy for high value-added products.
The objectives of the project are developing biotechnological tools to eliminate undesirable wood colors,
produce attractive and consistent wood colors and patterns, and increase the average value of the
hardwood lumber product mix.
2
Introduction
Wood color has a great economical impact on wood products. The hardwood lumber industry is facing a
particular increase in demand by their customers for wood with an attractive, consistent and specified
color. For many hardwood species, bright white is the typically preferred color in the lumber market. For
example, the white color of sugar maple and yellow birch is highly preferred by furniture plants, but the
light brown or yellowish brown color is less desirable for the industry. Wood products produced from
bright white maple wood are expensive. Consequently, discoloration greatly reduces their market value.
However, for other wood species such as black cherry, uniform reddish heartwood is the preferable color
for end users.
Wood color is produced by progressive accumulation of wood cells with a complex of diverse substances
called extractives during tree growing. Pigmented extractives determine most of the visual appearance
quality of hardwood species; therefore, they affect wood usefulness and value of the wood products.
Many recognizable and commercially desirable qualities of heartwood such as cherry, walnut and
rosewood are a result of the presence of pigmented extractives. The presence of pigmented extractives is
mostly distributed in the heartwood of trees. In some species such as maple or spruce, the extractives are
light color, and the heartwood of these species remains of a light color similar to the sapwood: these wood
species are called light heartwood trees. In some other species such as oak or cedar, the extractives
presented in heartwood are of dark color; therefore, the heartwood has various color intensities and can be
visually recognized from sapwood. These trees are described as regular heartwood trees.
Wood discoloration is a deep or shallow change in color that diverges from the natural wood color, and it
often affects wood value. Some aspects of wood discoloration have been studied extensively, but for other
aspects such as some particular causes and prevention remain elusive. Discolorations can occur in both
sapwood and heartwood of any wood species. Based on their causes, wood discoloration can be grouped
into two major categories: biological and chemical. Biological discoloration is caused by microorganisms, such as bluestain. Chemical discoloration is often referred as chemical or enzymatic stains that
often occur in heartwood. Chemical interactions related to color occur between phenolic extractives and
enzymes in the wood. These interactions can occur at any stage in the wood processing chain, including
standing trees, green logs, green or kiln-dried lumber and on wood products in service.
Most common methods for coloring wood products are using pigments or dye materials, which are carried
either in a liquid solution or as dispersion. For decolorizing stained wood products, currently there is no
effective method except for using bleaching chemicals. Using biological method for coloring or
decolorizing wood with fungi is a new innovative approach that has a great potential to produce
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preferable wood colors and patterns. Technology developed in this study will increase wood market value
and enhance the utilization of wood products in competitive marketing of Canadian lumber and furniture
manufacturing.
3
Background
Fungi are a specific group of micro-organisms that can affect wood color. Fungal infection of wood can
cause wood lighter, darker or other colors (Okino et al. 2009). The well-known fungal discoloration of
wood is called bluestain (Forest Products Laboratory 2002). Bluestain is caused by a particular group of
fungi that commonly attack only the sapwood of trees to bluish or greyish discoloration of the wood;
therefore, it is also called sapstain. This type of fungi utilizes simple sugars and starches presented in the
sapwood as nutrients and produce dark pigment called melanin during their growth. The wood
discoloration caused by fungal melanin may cover the whole sapwood or may appear as streaks or patches
of bluish to black intensities (Yang 2001). However, the bluish black wood color resulted from these
fungi is not desirable for wood end users. Most studies on wood blue stain focused on preventing or
controlling color development on wood products. One of such approaches is inoculating wood with a
colorless mutant of a sapstain fungus such as Ophiostoma piliferum, and the preoccupation of wood
surfaces by the colorless fungus can prevent later invasion of wood by staining fungi and thereafter,
wood color change. No study has been conducted to artificially inoculate bluestain fungi to produce
bluish black wood color for high wood value use.
Another wood color change caused by fungal infection is a green color caused by Chlorociboria species.
The wood discoloration is caused by the production of a fungal pigment xylindein, which is classified as a
napthaquinone. The naturally green-stained wood had been used as woodcrafts in European countries
since 14th - 15th century.
Wood decay can also change wood color (Robinson et al. 2007). A well-known example is called spalted
wood and is in high demand in the decorative wood market (Forest Products Laboratory 2004). Certain
decay fungi growing in wood (white-rot) cause Spalted wood. The decay fungal attack can cause random
patches of contrasting colors to appear on the surface of some hardwoods such as maple and birch. In
addition, when two or more competing fungi are meeting together in wood, it may create brown to black
zone lines on wood in the border of each fungal territories. In this way, spalted wood forms map-like
figures of different shapes and color contrasts. It may also produce unusual multicoloured streaks on
wood caused by reaction between the wood and decay fungi. However, the pattern and color changes
produced on spalted wood by these decay fungi are not predictable and repeatable. Still some fungi
produce various colorful metabolites during their growth (Schanel 2005). In dyeing and texture industry,
many colors are extracted from fungi.
Some fungi have ability to produce bleaching enzymes or are capable of enzymatic interactions with
wood compounds for decolorizing wood colors (Beggs et al. 2001). These enzymes (oxidases) are capable
of generating bleaching chemicals such as hydrogen peroxide when reacting with some wood
components. For example, fungi produce glucose oxidase that react with glucose in wood and then
produce hydrogen peroxide for bleaching wood stains.
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4
Staff
Dian-Qing Yang
Manon Gignac
Stéphanie Houde
5
Mycologist and Wood Protection Scientist, Project Leader
Wood Protection Scientist
Wood Protection Technologist
Materials and Methods
All measures were done in general agreement with the specified standards and protocols. The precision
levels were in accordance with the technical requirements.
5.1
Coloring wood with fungi
5.1.1
Selection of fungal species for coloring
Selection of fungal species for coloring wood was performed in Petri plates (85 mm in diameter) holding
20 ml of a 2% (w/v) malt extract agar medium in each plate. One mycelial plug (5 mm in diameter) was
cut from each fungal colony and transferred to the middle of each plate. The plates were sealed with a
Parafilm and incubated at 25°C and 75% RH for 14 days. The colors produced by these fungi on agar
were visually evaluated. Based on the principal colors produced by these fungi, 33 fungal species were
selected for testing on wood. The principal colors were pink, red, brown, orange, yellow, green, black,
blue and purple, each color contained 1 to 5 fungal species (Figure 1). The selected fungal species and
associated colors in agar plates are shown in Table 1.
Table 1
Selected fungal species from agar plate test
Number Fungal code
Fungal species
Color on agar
1
659B
Penicillium variabile Sopp
Red
2
750A
Fusarium culmorum (W. G. Sm.) Sacc.
Red
3
239A
Coryne microspora Ellis & Everh.
Light brown
4
430A
Diatrypella placena Rehm
Light brown
5
706B
Arthrographis cuboidea (Sacc. et Ellis) Sigler
Light brown
6
110A
Poria aurea Peck
Brown
7
534A
Corticium polosum Burt
Brown
8
795A
Lentinus cyathiformis Bres.
Brown
9
893A
Lecythophora hoffmannii (van Beyma) W. Gams & McGinnis
Brown
10
79A
Tyromyces balsameus (Peck) Murrill
Dark brown
11
473C
Trogia crispa Fr.
Dark brown
12
482B
Polyporus dryophilus Berk.
Dark brown
13
483A
Polyporus dryophilus var. vulpinus (Fr.) Overh.
Dark brown
14
840A
Peniophora piceae (Pers.) J. Erikss.
Dark brown
15
306D
Sporotrichum dimorphosporum v. Arx.
Yellow
16
790A
Gliocladium verticilloides Pidoplichko
Yellow
17
843C
Nectria ochroleuca (Schweinitz) Berkeley
Yellow
Yellowish
18
585E
Trichoderma atroviride P. Karst.
orange
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Number Fungal code
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
872B
164C
401A
197P
387AN
132I
772A
828A
837A
754A
597A
669A
31A
392A
433A
Fungal species
Trichoderma sp.
Verticillium sp.
Chlorosplenium aeruginascens (Nyl.) Karst
Scytalidium lignicola Pesante
Ophiostoma piceae (Münch) Syd., H. & P. Syd.
Aureobasidium pullulans (deBary) Arnaud
Phialophora alba von Beyma
Penicillium expansum Link
Penicillium implicatum Biourge
Fusarium verticillioides (Sacc.) Nirenberg
Dactylium dendroides (Bulliard) Fr.
Phialemonium dimorphosporum W. Gams & W. B. Cooke
Fusarium oxysporum Schlechtend.:Fr.
Ascocoryne cylichnium (Tul.) Korf
Cephalotheca purpurea (Shear) Chesters
Color on agar
Yellowish
orange
Green
Green
Dark blue
Dark blue
Black
Pink
Pink
Pink
Light purple
Purple
Purple
Dark purple
Dark purple
Dark purple
Figure 1 Agar cultures of fungi used for wood coloring test
All these fungal species came from the Culture Collection of wood-inhabiting fungi (FTK) held by
FPInnovations-Wood Products Division, Québec, Canada. All fungal cultures were maintained in a
liquid nitrogen reservoir for cryopreservation at -198°C before use.
5.1.2
Preparation of fungal solutions and wood specimens for coloring
The selected fungal species were retrieved from the liquid nitrogen reservoir and grown on a 2% malt
extract agar medium in Petri plates at 25°C for one week. Mycelial plugs (5 mm in diameter) were cut
from each fungal colony and transferred 3 plugs to each 125 ml flask containing 50 ml of a sterile 1.5%
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Difco malt extract broth (Becton, Dickinson and Company, Sparks, MD, USA) in distilled water (Figure
2). After incubation, the fungal cultures were homogenized into a fine mycelial section and spore
suspension that contained 1 x 106-8 spores/mycelial sections per ml of the solution. These fungal
suspensions were used immediately to treat wood specimens (Figure 3).
A local Quebec company provided fresh log sections of sugar maple (Acer saccharum Marshall), white
birch (Betula papyrifera Marshall) and yellow birch (Betula alleghaniensis Britton). The sapwood and
heartwood of log sections were identified and cut separately into wood specimens at the size of 60 mm x
20 mm x 5 mm. A total of 792 wood samples were prepared from these 3 wood species for testing
selected 33 fungal species.
Figure 2 Transferring agar cultures to liquid cultures for wood coloring test
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Figure 3 Fungal liquid cultures for wood coloring test
5.1.3
Treatment of wood specimens and evaluation
Wood specimens were placed in containers based on wood species and autoclaved at 121°C for 10
minutes. After cooling, wood specimens were dipped for 30 seconds in a fungal solution, 4 specimens per
treatment (Figure 4). Following the treatment, two pieces of specimens were placed on a W-shaped glass
support sitting over 2 layers of wet filter paper in a Petri plate. These plates were incubated in a growth
chamber set at 25C and 75% RH. Wood specimens were visually inspected for wood color change each
week up to 4 weeks. At the end of the test, two of the four wood specimens were dried at 50°C and the
other two were dried at 105°C. The final wood color evaluation of sapwood and heartwood specimens
after fungal treatment and drying were performed with a colorimeter (Color-guide 45/0 de BYK-Gardner
USA). The color penetration into the wood was visually evaluated by planing sample surfaces and edges.
Some samples were exposed to indoor sunlight for 6 months, and color changes on each sample were
monitored each month with the colorimeter.
Colors are perceived as combinations of green and yellow, red and blue, and red and yellow. Based upon
the equation of the CIE 1976 L*a*b* color space system, colors are assigned to a rectangular coordinate
system. The color coordinates are L* the lightness coordinate, a* the red/green coordinate (a+ indicating
red and –a* indicating green), and b* the yellow*/blue coordinate (+b* indicating yellow and –b*
indicating blue). Because the CIE L*a*b* colors space system is three-dimensional, it can often be
difficult to relate actual differences in color values to visually perceived differences. One method
developed for examining color differences uses the color metric difference (∆E*ab ) where :
_______________________________
∆E*ab = √ ((L*1-L*2)2 + (a*1-a*2)2 + (b*1-b*2)2)
Mathematically, the color metric difference (∆E*ab) is the Euclidean distance between two colors,
L*1a*1b*1 and L*2a*2b*2. It is relatively proportional to color differences perceived by human observers
(Billmeyer and Saltzman 1981). Haeghen et al. (2000) determine that ∆E*ab color difference values less
than 3 are considered unnoticeable to the human eye.
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In a study on white beech looking at color problems with the drying process (Rodolfo et al. 2007), the
magnitude of ∆E* was classified according to the grading rules as follows:
0.2 < ΔE* = Not visible difference
0.2 < ΔE* < 2 = Small difference
2 < ΔE* < 3 = Color difference visible with high quality screen
3 < ΔE* < 6 = Color difference visible with medium quality screen
6 < ΔE* < 12 = High color difference
ΔE* > 12 = Different colors
With this classification, ΔE* > 6 correspond to a high color difference and if >12 as different colors.
Figure 4 Treatment of wood samples with fungal liquid cultures for coloring
5.1.4
Effects of treatment conditions on wood coloring quality
The fungi used for examining the effects of treatment conditions on wood coloration were selected from
the most promising species after the preliminary test on wood and included 15 fungal species (Table 2).
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Table 2
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Fungal species used for coloring wood at different treatment conditions
Fungal code
706B
110A
483A
840A
164C
401A
197P
473C
132I
754A
829A
597A
669A
392A
433A
Fungal species
Arthrographis cuboidea
Poria aurea
Polyporus dryophilus var. vulpinus
Peniophora piceae
Verticillium sp.
Chlorosplenium aeruginascens
Scytalidium lignicola
Trogia crispa
Aureobasidium pullulans
Fusarium verticillioides
Ascocoryne solitario
Dactylium dendroides
Phialemonium dimorphosporum
Ascocoryne cylichnium
Cephalotheca purpurea
Color on wood
Red
Red
Brown (spalted)
Brown
Green
Green
Grey-blue
Brown (spot)
Black
Brown
Purple
Purple
Purple
Brown
Brown (spot)
The fungal inoculums and wood specimens used for treatments were prepared the same way as previously
described in section 5.1.2. Each group of wood samples was divided into 4 treatment conditions:
1) Wood samples were autoclaved at 121°C for 10 minutes and, after cooling, were dipped for 30
seconds in a fungal solution;
2) Wood samples were not autoclaved and dipped for 30 seconds in a fungal solution;
3) Wood samples were autoclaved at 121°C for 10 minutes and, after cooling, were vacuum
impregnated in a fungal solution for 20 minutes; and
4) Wood samples were not autoclaved and were vacuum impregnated in a fungal solution for 20
minutes.
This experiment contained 15 fungal species, 3 wood species (sugar maple, white birch and yellow birch),
2 wood types (sapwood and heartwood), 4 treatments, 2 replicates, and a total of 720 specimens were
used. After treatment, all specimens were placed in 2 covered unsterile plastic containers. These
containers were incubated in a growth chamber set at 25C and 75% RH. Wood specimens were visually
inspected for wood color change each week up to 2 weeks. At the end of the test, all wood specimens
were dried at 50°C, and the final wood colors were evaluated with a colorimeter in the same way as
previously described.
5.1.5
Production of multiple colors on wood
The fungi used for this experiment were 8 species selected from the most promising species after the
preliminary test on wood (Table 3).
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Table 3
Fungal species used for producing multiple colors on wood
Number
1
2
3
4
5
6
7
8
Fungal code
706B
483A
840A
401A
473C
754A
597A
387AN
Fungal species
Peniophora piceae
Trogia crispa
Ophiostoma piceae
Color on wood
Red
Brown (spalted)
Brown
Green
Brown (spot)
Brown
Purple
Dark blue
The fungal inoculums used for treatments were prepared the same way as previouslydescribed in section
5.1.2. The wood specimens were cut from sapwood of sugar maple at the size of 60 mm x 20 mm x 5
mm. Wood specimens were placed on a W-shaped glass support sitting over 2 layers of wet filter paper
in a Petri plate, 2 pieces of specimens per plate by wood species and autoclaved at 121°C for 10 minutes.
After cooling, wood specimens were dipped for 30 seconds in one of the 6 fungal solutions listed in
Table 3, except for Arthrographis cuboidea (706B) and Dactylium dendroides (597A). After the fungal
solution was completely absorbed by the wood 1 hour later, 100 μl each of the 2 other fungal solutions A.
cuboidea (706B) and D. dendroides (597A) were equally striped on the middle section of each specimen,
4 specimens per treatment. On the other 4 wood specimens, 1 drop (50 μl) of each of the 8 fungal
solutions listed in Table 3 was applied on one side of each specimen in 2 rows at equal distance of each
other. After treatment, these plates were incubated in a growth chamber set at 25C and 75% RH for
4 weeks. At the end of the test, all wood specimens were dried at 50°C and the final wood colors were
visually evaluated.
5.2
Decolorizing wood stain with fungi
5.2.1
Preparation of fungal materials
A literature search on microorganisms that could produce bleach enzymes was conducted. Based on
recorded information and particular fungal physical characterizations, 20 fungal species were selected for
testing on wood, including 6 Ascomycetes species and 14 Basidiomycetes species (Table 4).
The selected fungal species were grown on a 2% malt extract agar medium in Petri plates at 25°C for one
week. Mycelial plugs (5 mm in diameter) were cut from each fungal colony and transferred 3 plugs in
each 125 ml flask containing 50 ml of a sterile 1.5% Difco malt extract broth in distilled water. After
incubation, the fungal cultures were homogenized into a fine mycelial section and spore suspension that
contained 1 x 106-8 spores/mycelial sections per ml of the solution. These fungal suspensions were used
immediately to treat wood specimens.
9 of 50
Table 4
Selected fungal species for decolorizing wood stains
Number Fungal code
Fungal species
1
392A
Ascocoryne cylichnium (Tul.) Korf.
2
75A
Bjerkandera adusta (Willd.) P. Karst.
3
105A
Coriolus versicolor (L.:Fr.) Quél.
4
857A
Lentinus edodes (Berk.) Pegler
5
52A
Merulius tremellosus (Schrad.:Fr.) Fr.
6
173A
Mollisia caesia Sacc.
7
700A
Ophiostoma flexuosum Solheim
8
271A
Ophiostoma multiannulatum (Hedgc. & Davidson) Hendr.
9
815A
Ophiostoma tetropii Mathiesen
10
284A
Phanerochaete chrysosporium Burdsall
11
345A
Phlebia radiata Fries
12
897A
Phlebiopsis gigantea (Fr.) Jülich
13
71A
Pleurotus ostreatus (Jacq.:Fr.) Kummer
14
569A
Pleurotus ulmarius (Fr.) Kummer
15
480A
Polyporus dichrous Fries
16
323C
Poria subvermispora Pilat
17
523A
Poria obliqua (Pers.:Fr.) Karst.
18
82A
Pycnoporus cinnabarinus (Jacq.:Fr.) P. Karst.
19
718A
Sporothrix sp.
20
473C
Trogia crispa Fries
5.2.2
Fungal class
Ascomycetes
Basidiomycetes
Basidiomycetes
Basidiomycetes
Basidiomycetes
Ascomycetes
Ascomycetes
Ascomycetes
Ascomycetes
Basidiomycetes
Basidiomycetes
Basidiomycetes
Basidiomycetes
Basidiomycetes
Basidiomycetes
Basidiomycetes
Basidiomycetes
Basidiomycetes
Ascomycetes
Basidiomycetes
Preparation of wood specimens for treatment
Stained wood (either chemical stain or biological stain) of sugar maple, yellow birch and white pine were
obtained from sawmills (Figures 5-6). Wood samples were cut into wafer size 80 mm x 30 mm x 5 mm
from selected stained wood. Wood color of each sample was then recorded with a colorimeter. Based on
wood species, samples were soaked in sterile water for 24 hours to obtain a moisture content of 50-80%
before the treatment.
10 of 50
Figure 5 Blue stain (top) and coffee stain (bottom) of white pine samples used in the test
Figure 6 Internal stain and end stain wood samples of sugar maple (top) and yellow birch
(bottom) used in the test
5.2.3
Treatment of wood specimens and evaluation
Wood specimens were autoclaved at 121°C for 10 minutes. After cooling, the specimens were dipped
half section of the sample in a fungal solution (Figure 7), and the other half section of the sample served
as untreated control. This test contained 20 fungal species, 3 wood species (sugar maple, yellow birch and
white pine), 4 replicates, and a total of 240 specimens were used. Treated wood samples were put in a
Petri plate (14-cm dia.), 2 pieces per plate, on a W-shaped glass support sitting over 2 layers of wet filter
paper in the plate. The plates were placed at 25°C and 75% RH for incubation. The fungal growth and
wood color change on each sample were visually evaluated each week up to 8 weeks. At the end, all
wood samples were oven dried to dryness at 60°C, and then the color differences between treated and
untreated sections of wood samples were recorded with a colorimeter.
11 of 50
Figure 7 Treatment of wood samples with fungal liquid cultures for decolorizing unpleasant
wood color
6
Results
6.1
Coloring wood with pigmented fungal species
6.1.1
Wood coloring with selected fungal species
The results of wood coloring with selected fungal species are shown in Table 5. In most cases, one fungal
species colored all three wood species tested into a similar color such as red, brown, green, purple and
black (Figure 8). In addition to wood species, most of the fungal species colored sapwood and heartwood
of a wood species at a similar intensity level (Figures 9 and 10). Therefore, wood colors shown in
Table 5 represented the major color observed from all wood specimens treated with each fungal species.
Some fungi not only changed wood color, but also produced different patterns, such as spot wood pattern
produced by the fungus Trogia crispa (473C) (Figure 11) and spalted wood pattern produced by the
fungus Polyporus dryophilus var. vulpinus (483A) (Figure 12).
Because of the interference of wood cells, the colors shown on agar may or may not be the same as the
one shown on wood. For example, both agar and wood were colored into green by Verticillium sp. (164C)
and Chlorosplenium aeruginascens (401A); colored into purple by Dactylium dendroides (597A) and
Phialemonium dimorphosporum (669A); colored into brown by Trogia crispa (473C) and Polyporus
dryophilus var. vulpinus (483A); and colored into black by Aureobasidium pullulans (132I). Some fungal
species produced different colors on agar and on wood. For example, Fusarium culmorum (750A)
produced red color on agar, but purple on wood; and Fusarium oxysporum (31A) produced dark purple
color on agar, but brown on wood. Other fungal species produced a similar color on agar, but different
colors on wood. For examples, both Phialophora alba (772A) and Penicillium expansum (828A)
produced pink pigment on agar, but on wood the former caused light brown and the later caused greyish
color. Still some fungal species produced different colors on agar, but a similar color on wood. For
12 of 50
example, Arthrographis cuboidea (706B) produced light brown and Poria aurea (110A) produced brown
color on agar, but both species produced red color on wood. There were several fungal species that
produced pigments on agar, but not on wood. For example, in agar plate cultures Penicillium variabile
(659B) produced red pigment, Coryne microspora (239A) produced light brown pigment, and
Sporotrichum dimorphosporum (306D) produced yellow pigment, while none of them produced any color
on wood.
In general, wood specimens dried at different temperatures did not significantly change principal wood
colors, but significantly changed color lightness. The wood specimens dried at 105°C were significantly
darker than those dried at 50°C. The example of such color changes is shown in Figure 13 as red color
stained by Poria aurea (110A) and dried at 50°C and 105°C.
13 of 50
Table 5
Fungal coloring on wood specimens
Number Fungal code
Fungal species
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
659B
750A
239A
430A
706B
110A
534A
795A
893A
79A
473C
482B
483A
840A
306D
Penicillium variabile Sopp
Fusarium culmorum (W. G. Sm.) Sacc.
Coryne microspora Ellis & Everh.
Diatrypella placena Rehm
Arthrographis cuboidea (Sacc. et Ellis) Sigler
Poria aurea Peck
Corticium polosum Burt
Lentinus cyathiformis Bres.
Lecythophora hoffmannii (van Beyma) W. Gams & McGinnis
Tyromyces balsameus (Peck) Murrill
Trogia crispa Fr.
Polyporus dryophilus Berk.
Polyporus dryophilus var. vulpinus (Fr.) Overh.
Peniophora piceae (Pers.) J. Erikss.
Sporotrichum dimorphosporum v. Arx.
16
790A
Gliocladium verticilloides Pidoplichko
17
843C
Nectria ochroleuca (Schweinitz) Berkeley
18
585E
Trichoderma atroviride P. Karst.
19
20
21
22
872B
164C
401A
197P
Trichoderma sp.
Verticillium sp.
Chlorosplenium aeruginascens (Nyl.) Karst
Scytalidium lignicola Pesante
23
24
25
26
27
28
29
30
31
387AN
132I
772A
828A
837A
754A
597A
669A
31A
Ophiostoma piceae (Münch) Syd., H. & P. Syd.
Aureobasidium pullulans (deBary) Arnaud
Phialophora alba von Beyma
Penicillium expansum Link
Penicillium implicatum Biourge
Fusarium verticillioides (Sacc.) Nirenberg
Dactylium dendroides (Bulliard) Fr.
Phialemonium dimorphosporum W. Gams & W. B. Cooke
Fusarium oxysporum Schlechtend.:Fr.
32
33
392A
433A
Ascocoryne cylichnium (Tul.) Korf
Cephalotheca purpurea (Shear) Chesters
Color on
wood
No color
Purple
No color
No color
Red
Red
Brown
Brown
Brown
Brown
Brown spot
Brown
Brown spalted
Brown
No color
Greyish
yellow
Greyish
yellow
Greyish
brown
Yellowish
brown
Green
Green
Greyish blue
Greyish
brown
Black
Light Brown
Grey
Green
Light Brown
Purple
Purple
Brown
Brownish
purple
Brown spot
14 of 50
Figure 8 Coloration of wood samples with fungi
15 of 50
Figure 9 Fungal coloration (red) on heartwood and sapwood of sugar maple
Color change by Poria aurea
(red on wood)
L*
Chromatic coordinates (L*, a*, b*)
100
90
80
70
60
50
40
b*
30
20
a*
10
Heart
Sap
Heart
Sugar maple
Sap
White birch
L*
a*
a*
b*
Heart
Poria
aurea
Control
Poria
aurea
Control
Poria
aurea
Control
Poria
aurea
Control
Poria
aurea
Control
Poria
aurea
Control
0
Sap
Yellow birch
b*
L*
Figure 10 Color changes of wood samples caused by fungus Poria aurea
16 of 50
Figure 11 Spot wood pattern produced by fungus Trogia crispa
Figure 12 Spalted wood pattern produced by fungus Polyporus dryophilus var. vulpinus
17 of 50
Color change
Poria aurea (110A)
25,0
50°C
105°C
20,0
∆E*
15,0
10,0
5,0
0,0
Sap
Heart
Sugar maple
Sap
Heart
White birch
Sap
Heart
Yellow birch (Merisier)
Figure 13 Red color changes of wood samples dried at different temperatures
6.1.2
Color variations on sapwood and heartwood of three treated wood species
Color variations (ΔE*) of all fungus-treated wood samples compared with the untreated controls are
presented in Table 6. All of the fungal treatments lead to a significant color change of the three hardwood
species, both on sapwood and heartwood, with ΔE* values ranging from 25.2 up to 73.6.
The wood color variations between sapwood and heartwood of a wood species were also evaluated, and
some representative colors are shown in Figures 14 to 23. Most of the treated samples had a ΔE* value
difference between sapwood and heartwood below 10. The degree of the color difference between
sapwood and heartwood was more depending on colors and wood species. For example, brown color
showed the minimum variations between sapwood and heartwood of the all three wood species
(Figure 14) with ΔE* values less than 3 and can not be noticed by necked eyes, whereas green color had
the largest ΔE* variations between 5.3 and 8.3 (Figure 23). Among the 3 wood species tested, sugar
maple showed the minimum variations between sapwood and heartwood for purple and green colors
(Figures 19 and 23) and the maximum for black and red colors (Figures 17 and 21); white birch showed
the minimum variations for grey and black colors (Figures 15 and 17) and the maximum for purple color
(Figure 19); and yellow birch showed the minimum variations for brown and red colors (Figures 14
and 21) and the maximum for green color (Figure 23).
18 of 50
Table 6
Fungal code
110A
132I
164C
197P
239A
306D
31A
387AN
392A
401A
430A
433A
473C
482B
483A
534A
585E
597A
659B
669A
706B
750A
754A
772A
790A
795A
79A
828A
837A
840A
843C
872B
893A
Wood color change (ΔE*) after fungal treatment and drying
Fungal name
Poria aurea
Aureobsidium pullulans
Verticillium sp.
Coryne microspora
Sporotrichum dimorphosporum
Fusarium oxysporum
Ophiostoma piceae
Ascocorune cylichnium
Diatrypella placena
Trogia crispa
Polyporus dryophilus
Corticium polosum
Trichoderma atroviride
Penicillium variabile
Fusarium culmorum
Phialophora alba
Gliocladium verticilloides
Lentinus cyathiformis
Tyromoces balsameus
Penicillium expansum
Penicillium implicatum
Peniophora piceae
Nectria ochroleuca
Trichoderna sp.
Lecythophora hoffmannii
Sugar maple
heartwood sapwood
57.1
35
59.4
46.1
64.7
62.7
55.2
59.7
40.2
57.3
64.8
60.3
56.2
64.6
41.3
65.6
62.7
64.2
65.2
49.7
42
61.4
54.8
68
66
61.4
64.6
60.5
52.3
54.4
63.2
58.5
65.3
52.5
33.5
55.8
52.1
65.9
66.5
61.5
60.5
25.2
62.8
70.9
63.8
60.8
67.5
65.8
61.3
68.6
65.6
69.3
44.9
48
52.1
60.6
73.6
68
59.3
66
59.3
52.1
60.3
71.9
71.3
69.5
White birch
heartwood sapwood
56.5
46.1
56.1
45.8
67.3
63.2
61.9
61.1
55.7
59
69.6
60.9
59.2
66.7
42.6
65.1
57.3
55.9
61
48.4
37.1
61.4
65.3
65.9
65.1
57.4
71
63.8
53.2
59.4
61.7
61.7
64.6
55.1
44.5
59.5
39.4
66.7
68.8
59.5
53.6
54.5
61.5
70.1
58.8
58.3
61.8
44.1
66
63.8
52.3
66.1
65
39.9
62
63.3
67.3
71.8
63.1
70
61
51.3
62.9
72.4
65.7
69.7
Yellow birch
heartwood sapwood
60.3
47.6
57.4
51.5
63.9
58.7
58.7
54.6
54.6
59.1
61.9
56.6
57.1
64.8
47.9
54.1
55.6
54.6
64.4
51
42.2
59.3
57.2
60.8
67.4
54.4
64.3
65.5
48.1
56.2
64.6
57.7
65.2
46.4
43
57.7
41.9
68.1
68
60.5
54.1
49.3
57.2
70.4
62.7
56.6
66.7
58.2
60.3
64.6
51.1
63.6
59.3
40.4
58.9
60.6
69.6
69.3
57.2
66.3
62.1
58.9
68.7
68.6
66.2
66.4
19 of 50
12,0
∆E* (sapwood vs heartwood)
10,0
8,0
6,0
4,0
2,7
2,5
1,1
2,0
0,0
Sugar m aple
Figure 14
White birch
Yellow birch
Brown wood color variation between sapwood and heartwood caused by
Trogia crispa (473C)
12,0
10,0
8,0
6,0
4,2
4,0
3,1
3,3
White birch
Yellow birch
2,0
0,0
Sugar m aple
Figure 15 Grey wood color variation between sapwood and heartwood caused by Penicillium
expansum (828A)
20 of 50
Figure 16 Visual appearance of black coloration of sugar maple sapwood (left) and
heartwood (right) caused by Aureobasidium pullulans
12,0
10,0
8,0
6,0
5,6
5,0
4,0
1,7
2,0
0,0
Sugar m aple
White birch
Yellow birch
Figure 17 Black wood color variation between sapwood and heartwood caused by
Aureobasidium pullulans (132I)
21 of 50
Figure 18 Visual appearance of purple coloration of yellow birch sapwood (left) and
heartwood (right) caused by Dactylium dendroides
12,0
10,0
7,2
8,0
6,0
4,3
4,0
3,2
2,0
0,0
Sugar m aple
White birch
Yellow birch
Figure 19 Purple wood color variation between sapwood and heartwood caused by Dactylium
dendroides (597A)
22 of 50
Figure 20 Visual appearance of red coloration of white birch sapwood (left) and heartwood
(right) caused by Arthrographis cuboidea
12,0
10,0
8,0
7,8
6,0
4,5
4,0
2,9
2,0
0,0
Sugar m aple
White birch
Yellow birch
Figure 21 Red wood color variation between sapwood and heartwood caused by
Arthrographis cuboidea (706B)
23 of 50
Figure 22 Visual appearance of green coloration of sugar maple sapwood (left) and
heartwood (right) caused by Chlorosplenium aeruginascens
12,0
10,0
8,3
8,0
6,0
7,0
5,3
4,0
2,0
0,0
Sugar m aple
White birch
Yellow birch
Figure 23 Green wood color variation between sapwood and heartwood caused by
Chlorosplenium aeruginascens (401A)
6.1.3
Color uniformity and penetration into wood
The promising fungal species for coloring wood are shown in Table 7. After incubation for 4 weeks,
many wood samples were totally colored into another color (Figure 24), such as green color stained by
C. aeruginascens and P. implicatum; black color stained by A. pullulans; grey color stained by
P. expansum; and brown color stained by F. verticillioides and F. oxysporum. The remaining fungi
colored over 75% of the wood surface area during this incubation period.
24 of 50
Among the 17 promising fungal species, 11 species were able to penetrate colors into wood, whereas 6
species only colored wood surfaces (Table 7, Figure 25). The fungal species that penetrated into wood
have more commercial potential and value than the species that only remained on wood surfaces.
Table 7
Fungal color uniformity and penetration into wood
Fungal code
Fungal species
Color on
wood
Uniformity (0-5)1
Penetration2
706B
Red
4.9
P
110A
Poria aurea
Red
3.7
P
473C
Trogia crispa
Brown
4.8
S
483A
Brown
4.8
P
164C
Verticillium sp.
Green
4.7
P
401A
Green
5
P
197P
4.3
P
387AN
Ophiostoma piceae
Greyish blue
Greyish
brown
4.9
P
132I
Aureobasidium pullulans
Black
5
P
828A
Penicillium expansum
Grey
5
S
837A
Penicillium implicatum
Green
5
S
754A
Light Brown
5
S
597A
Purple
4.2
P
669A
Purple
4.1
P
31A
Fusarium oxysporum
5
S
392A
Brown
Brownish
purple
4
P
433A
Light Brown
4.6
S
1
2
0 = 0% color coverage; 1 = <25% color coverage; 2 = 25% to <50% color coverage; 3 = 50% to <75% color
coverage; 4 = 75% to <100% color coverage, and 5 = 100% color coverage.
P = penetrate into wood; S = remain on wood surface.
25 of 50
Figure 24 Uniformity of wood samples stained with A. cuboidea (red) and C. aeruginascens
(green)
Figure 25 Penetration of red color into wood stained by A. cuboidea
26 of 50
6.1.4
Color resistance to weathering
The results of weathering various wood samples under natural indoor sunlight exposure are presented in
Figures 26-33. After 6 months of indoor sunlight exposure, untreated wood samples had the minimum
effect from sunlight; with a ∆E* value less than 6. Among the 3 wood species tested, white birch wood
was the most resistant to sunlight, with a ∆E* value less than 3, unnoticeable to the naked eye
(Figure 26). Among fungus colored wood, black color was the most resistant to weathering with ∆E*
values between 5 and 6 (Figure 27), followed by green color with ∆E* values between 8 and 10
(Figure 28). The other colors such as purple (Figure 29), red (Figure 30), light brown (Figure 31) and
brown (Figure 32) had similar resistance to sunlight, with ∆E* values between 10 and 12. Grey color was
the most susceptible to sunlight weathering, with ∆E* values between 12 and 14 in 6 months (Figure 33).
6
Sugar maple
White birch
5
Yellow birch
4
?E*
3
2
1
0
5
9
13
17
21
25
Weathering time (weeks)
Figure 26 Color changes of untreated wood samples at different weathering times
27 of 50
6
Sugar maple
White birch
5
Yellow birch
∆E*
4
3
2
1
0
5
9
13
17
21
25
Figure 27 Black color changes of wood samples treated with fungal strain 132I at different
weathering times
12
Sugar maple
White birch
10
Yellow birch
∆E*
8
6
4
2
0
5
9
13
17
21
25
Figure 28 Green color changes of wood samples treated with fungal strain 401A at different
weathering times
28 of 50
14
Sugar maple
12
White birch
Yellow birch
∆E*
10
8
6
4
2
0
5
9
13
17
21
25
Figure 29 Purple color changes of wood samples treated with fungal strain 597A at different
weathering times
14
Sugar maple
12
White birch
Yellow birch
∆E*
10
8
6
4
2
0
5
9
13
17
21
25
Figure 30 Red color changes of wood samples treated with fungal strain 110A at different
weathering times
29 of 50
14
Sugar maple
12
White birch
Yellow birch
∆E*
10
8
6
4
2
0
5
9
13
17
21
25
Figure 31 Light brown color changes of wood samples treated with fungal strain 754A at
different weathering times
12
Sugar maple
10
White birch
Yellow birch
∆E*
8
6
4
2
0
5
9
13
17
21
25
Figure 32 Brown color changes of wood samples treated with fungal strain 31A at different
weathering times
30 of 50
16
Sugar maple
14
12
White birch
Yellow birch
∆E*
10
8
6
4
2
0
5
9
13
17
21
25
Figure 33 Grey color changes of wood samples treated with fungal strain 828A at different
weathering times
6.1.5
Effects of treatment conditions on wood coloring quality
The effects of treatment conditions on the quality and uniformity of colored wood are presented in Tables
8-10. On sugar maple wood (Table 8), red color stained by Arthrographis cuboidea or Poria aurea and
purple color stained by Dactylium dendroides failed partially or totally on non-sterile samples; whereas
brown color stained by several fungal species failed on sterile samples. Vacuum process improved brown
color uniformity of sterile samples stained by Peniophora piceae, Trogia crispa or Fusarium
verticillioides, whereas no significant improvement was found by vacuum process on non-sterile samples.
On white birch wood (Table 9), it was poorly stained on non-sterile samples by P. aurea (red), P. piceae
(brown) and P. dimorphosporum (purple), whereas vacuum process improved red color uniformity of the
samples stained by A. cuboidea. On sterile samples, P. dryophilus, P. piceae and T. crispa partially or
totally failed to stain wood into brown color, whereas P. aurea failed to uniformly stain wood into red.
However, vacuum process improved brown color uniformity of the samples stained by P. dryophilus.
On yellow birch wood (Table 10), little stain was obtained on non-sterile samples by A. cuboidea (red),
P. aurea (red) and P. dimorphosporum (purple), especially on samples treated with vacuum process. On
sterile wood samples, several fungal species also failed to color wood into the designable colors, such as
A. cuboidea (red on heartwood), P. aurea (red on sapwood), P. piceae and F. verticillioides (brown on
sapwood). Vacuum process did not significantly improve any particular wood color quality and
uniformity in this wood species.
The results of color penetrations into wood samples with dipping or vacuum process are presented in
Tables 11-12. In most cases, color penetration into sapwood was slightly deeper than into heartwood
such as red color stained by A. cuboidea penetrated into sapwood by 2 mm and into heartwood by
1.25 mm after incubation for 2 weeks. However, vacuum process, in most cases, did not increase color
penetration into wood samples.
31 of 50
Table 8
Fungal coloring of sugar maple wood in different treatment conditions
Sterile
Fungal
code
Fungal
name
Wood
color
Wood
part
706B
Arthrographis
cuboidea
Red
110A
Poria aurea
483A
Polyporus
dryophilus
Red
Brown
Non-sterile
Dipping
1
Vacuum
2
Dipping
Vacuum
Coloration
%
Uniformity
(0-5)
Coloration
%
Uniformity
(0-5)
Coloration
%
4
100
4
0
0
100
2
4
100
5
0
0
100
2,5
100
3
50
4
0
0
0
0
Sap
100
3
100
2,5
0
0
0
0
Heart
50
5
50
5
100
5
100
2,5
Sap
0
0
0
0
100
4,5
100
3
0
0
100
4
100
3,5
100
5
Coloration
%
Uniformity
(0-5)
Heart
100
Sap
100
Heart
Uniformity
(0-5)
840A
Peniophora
piceae
Brown
Heart
Sap
0
0
100
5
50
3
100
4,5
164C
Verticillium sp.
Green
Heart
100
5
100
3
100
4
100
5
Sap
100
5
100
4,5
100
3
100
5
Heart
100
4,5
100
5
100
4
100
5
Sap
100
4,5
100
5
100
4,5
100
5
Heart
100
4,5
100
4,5
100
3,5
100
4,5
Sap
100
5
100
5
100
4
100
5
Heart
50
5
50
5
100
2,5
100
4,5
Sap
0
0
100
5
50
3
100
4,5
Heart
100
5
100
5
100
4
100
5
Sap
100
5
100
5
100
3,5
100
5
Heart
0
0
100
5
100
4,5
50
5
Sap
50
3
100
4
100
3,5
100
4,5
Heart
100
3
100
4,5
100
2,5
100
3
Sap
100
4
100
4
100
1,5
100
4
Heart
100
4,5
100
5
100
2
100
1
Sap
100
5
100
5
0
0
0
0
Heart
100
2,5
100
5
100
2,5
100
3
Sap
100
4
100
5
100
3
100
2,5
Heart
100
5
100
3,5
100
4,5
100
4,5
Sap
100
3,5
100
5
100
4,5
100
4
Heart
100
5
50
3
100
4
0
0
Sap
100
4,5
0
0
100
3
0
0
401A
Chlorosplenium
aeruginascens
197P
Scytalidium
lignicola
473C
132I
Trogia crispa
Aureobsidium
pullulans
754A
Fusarium
verticillioides
829A
Ascocorune
solitario
597A
Dactylium
dendroides
669A
Phialemonium
dimorphosporum
392A
Ascocorune
cylichnium
433A
Cephalotheca
purpurea
Green
Grey
Brown
Black
Brown
Purple
Purple
Purple
Brown
Brown
1
Percentage of wood samples changed color.
2
Rating scales of color uniformity on wood sample surfaces: 0 = 0% color coverage; 1 = <25% color coverage; 2 = 25% to <50%
color coverage; 3 = 50% to <75% color coverage; 4 = 75% to <100% color coverage, and 5 = 100% color coverage.
32 of 50
Table 9
Fungal coloring of white birch wood in different treatment conditions
Sterile
Fungal
code
Fungal
name
Wood
color
Wood
part
706B
Arthrographis
cuboidea
Red
110A
Poria aurea
483A
Polyporus
dryophilus
Red
Brown
Non-sterile
Dipping
1
Vacuum
2
Dipping
Vacuum
Coloration
%
Uniformity
(0-5)
Coloration
%
Uniformity
(0-5)
Coloration
%
4
100
5
100
3
100
5
5
100
5
0
0
100
4,5
50
3
100
2,5
0
0
0
0
Sap
0
0
100
2,5
100
3
0
0
Heart
50
5
100
5
100
5
100
4
Sap
0
0
100
4,5
0
0
100
2,5
0
0
0
0
0
0
50
5
2
Coloration
%
Uniformity
(0-5)
Heart
100
Sap
100
Heart
Uniformity
(0-5)
840A
Peniophora
piceae
Brown
Heart
Sap
0
0
100
3,5
0
0
50
164C
Verticillium sp.
Green
Heart
100
4,5
100
4,5
100
5
100
5
Sap
100
4
100
5
100
4,5
100
3,5
Heart
100
5
100
5
100
5
100
5
Sap
100
5
100
5
100
5
100
5
Heart
100
3,5
100
5
100
4,5
100
5
Sap
100
5
100
5
100
2
100
4,5
Heart
0
0
50
5
100
5
50
5
Sap
0
0
0
0
100
5
100
4,5
Heart
100
3,5
100
5
100
4
100
5
Sap
100
5
100
5
100
4,5
100
5
Heart
100
4,5
100
4
100
4
100
5
Sap
100
2,5
100
5
100
4
100
4,5
Heart
100
3,5
100
4
100
2,5
100
3
Sap
100
4
100
4
100
2,5
100
3
Heart
100
4,5
100
3
100
4
50
2
Sap
100
4
50
2
100
3
0
0
Heart
100
5
100
2
0
0
0
0
Sap
100
5
50
5
50
5
0
0
Heart
100
4
100
4,5
100
3
100
4,5
Sap
100
4,5
100
5
100
4
100
5
Heart
100
5
100
4,5
100
5
100
3,5
Sap
100
4
0
0
100
4
100
4,5
401A
Chlorosplenium
aeruginascens
197P
Scytalidium
lignicola
473C
132I
Trogia crispa
Aureobsidium
pullulans
754A
Fusarium
verticillioides
829A
Ascocorune
solitario
597A
Dactylium
dendroides
669A
Phialemonium
dimorphosporum
392A
Ascocorune
cylichnium
433A
Cephalotheca
purpurea
Green
Grey
Brown
Black
Brown
Purple
Purple
Purple
Brown
Brown
1
2
33 of 50
Table 10 Fungal coloring of yellow birch wood in different treatment conditions
Sterile
Fungal
code
Fungal
name
Wood
color
Wood
part
Non-sterile
Dipping
1
Vacuum
2
Dipping
Vacuum
Coloration
Uniformity
%
(0-5)
Coloration
%
Uniformity
(0-5)
Coloration
%
Uniformity
(0-5)
Coloration
%
Uniformity
(0-5)
706B
Arthrographis
cuboidea
Red
Heart
0
0
100
2,5
0
0
0
0
Sap
100
5
100
3,5
100
3
0
0
110A
Poria aurea
Red
Heart
100
3
0
0
50
4
0
0
Sap
0
0
100
3
50
2
0
0
50
3
50
5
100
5
483A
Polyporus
dryophilus
Brown
Heart
100
4,5
Sap
100
4,5
0
0
100
5
100
5
840A
Peniophora
piceae
Brown
Heart
100
4,5
100
5
100
4,5
100
5
Sap
0
0
100
4,5
50
3
100
5
164C
Verticillium sp.
Green
Heart
100
4
100
5
100
4
100
5
Sap
100
4
100
4,5
100
4
100
4
401A
Chlorosplenium
aeruginascens
Green
Heart
100
4
100
5
100
5
100
5
Sap
100
4
100
5
100
4
100
5
197P
Scytalidium
lignicola
Grey
Heart
100
4
100
5
100
5
100
5
Sap
100
5
100
5
100
4,5
100
5
473C
Trogia crispa
Brown
Heart
100
4,5
50
3
100
4,5
100
3,5
Sap
50
2
100
4
100
3
100
3
132I
Aureobsidium
pullulans
Heart
100
4
100
5
100
5
100
5
Sap
100
5
100
5
100
4,5
100
5
Heart
100
4,5
100
5
100
5
100
5
Sap
0
0
50
5
100
4
100
4,5
Heart
100
2,5
100
5
50
2
100
3
Sap
100
3
100
3,5
100
2
100
2
Heart
100
4
100
3,5
100
2,5
50
2
Sap
100
5
100
5
0
0
100
4,5
Heart
100
3
50
3
50
1
0
0
Sap
100
4
100
5
100
4
100
2
Heart
100
4,5
100
4,5
100
5
100
5
Sap
100
4,5
100
4,5
100
3
100
5
Heart
100
5
50
5
100
3,5
100
4,5
Sap
100
5
100
4,5
100
2,5
100
5
754A
Fusarium
verticillioides
829A
Ascocorune
solitario
597A
669A
392A
433A
Dactylium
dendroides
Phialemonium
dimorphosporum
Ascocorune
cylichnium
Cephalotheca
purpurea
Black
Brown
Purple
Purple
Purple
Brown
Brown
1
2
34 of 50
Table 11 Fungal color penetration into wood in different treatment conditions
Fungal
code
Fungal
name
Wood
color
706B
Red
Wood
species
Wood
part
Sugar maple
Heart
Sap
Heart
Sap
Heart
Sap
Heart
Sap
Heart
Sap
Heart
Sap
Heart
Sap
Heart
Sap
Heart
Sap
Heart
Sap
Heart
Sap
Heart
Sap
Heart
Sap
Heart
Sap
Heart
Sap
White birch
Yellow birch
401A
Green
Sugar maple
White birch
Yellow birch
132I
Black
Sugar maple
White birch
Yellow birch
754A
Brown
Sugar maple
White birch
Yellow birch
597A
Purple
Sugar maple
White birch
Yellow birch
Penetration (mm)
Dipping Vacuum
1,25
2
1
0,5
0,5
0,3
0,3
0,5
1
0,5
1
0,5
1
1,5
1
2
2
0,5
0,5
0,5
0,5
1
1
1
1
1
0,5
0,7
1
0,5
1
0,3
0,5
0,5
0,3
0,5
0,3
1
0,8
0,5
0,5
35 of 50
Table 12 Summary of fungal color penetration into wood in different treatment conditions
Fungal
code
Fungal
name
Wood
color
Wood
part
706B
Red
401A
Green
132I
Black
754A
Brown
597A
Purple
Heart
Sap
Heart
Sap
Heart
Sap
Heart
Sap
Heart
Sap
6.1.6
Penetration (mm)
Dipping
Vacuum
1,25
1
1,5
1,75
0,4
0,5
0,4
0,5
0,75
1
0,67
1
0,6
0,75
1
0,8
0,3
0,4
0,5
0,5
Production of multiple wood colors by the treatment
The results of the test on production of multiple colors on wood are shown in Table 13. A joint
inoculation of sugar maple wood with 3 or more fungal species produced 2 to 4 main colors on treated
wood. The 2 main colors produced were brown/red such as wood treated with fungal species 840A +
706B + 597A, or brown/purple such as wood treated with fungal species 754A + 706B + 597A. The 3
main colors produced were green/red/blue (Figure 34, treatment with fungal species 401A + 706B +
597A), or red/purple/green (Figure 35, treatment also with fungal species 401A + 706B + 597A), or
brown/red/purple (Figure 36, treatment with fungal species 387AN + 706B + 597A). The 4 main colors
produced were brown/red/purple/green such as wood treated with fungal species 483A + 706B + 597A
(Figure 37), or with 8 fungal species (Figure 38). It is noticed that one treatment could produced different
color patterns, such as wood specimens held in plate 1 produced 2 colors after the treatment with the
fungal species 483A + 706B + 597A, whereas it produced 4 colors on wood specimens held in plate 2 by
the same treatment. The similar situations were also observed on wood specimens treated with fungal
species 473A + 706B + 597A, or with 387AN + 706B + 597A. It is also noticed that a same treatment
could produce 2 types of color patterns; such as wood specimens treated with fungal species 401A +
706B + 597A produced green/red/blue colors in plate 1 but red/purple/green in plate 2.
The capability of producing multiple colors on wood by the treatment with several fungal species together
resulted in various rainbow wood patterns on treated wood (Figures 39-43). If these rainbow wood
patterns could be produced at a large industry scale, the wood value would be largely increased in the
decorative market.
36 of 50
Table 13 Multiple colors on wood by fungal treatment
Wood species
Plate
Treatment
Color on wood
Sugar maple
Sugar maple
Sugar maple
Sugar maple
Sugar maple
Sugar maple
Sugar maple
Sugar maple
Sugar maple
Sugar maple
Sugar maple
Sugar maple
Sugar maple
Sugar maple
1
2
1
2
1
2
1
2
1
2
1
2
1
2
483A + 706B + 597A
483A + 706B + 597A
840A + 706B + 597A
840A + 706B + 597A
401A + 706B + 597A
401A + 706B + 597A
473A + 706B + 597A
473A + 706B + 597A
754A + 706B + 597A
754A + 706B + 597A
387AN + 706B + 597A
387AN + 706B + 597A
8 fungal solutions
8 fungal solutions
Brown/red
Brown/red/purple/green
Brown/red
Brown/red
Green/red/blue
Red/purple/green
Brown/red
Brown/red/purple
Brown/purple
Brown/purple
Brown/red/purple
Brown/red
Figure 34 Multiple colors produced by the fungal species 401A + 706B + 597A
37 of 50
Figure 35 Multiple colors also produced by the fungal species 401A + 706B + 597A
Figure 36 Multiple colors produced by the fungal species 387AN + 706B + 597A
38 of 50
Figure 37 Multiple colors produced by the fungal species 483A + 706B + 597A
Figure 38 Multiple colors produced by 8 fungal species
39 of 50
Figure 39 Rainbow wood pattern produced by a joint treatment with fungal species 483A +
706B + 597A
Figure 40 Rainbow wood pattern produced by a joint treatment with fungal species 387AN +
706B + 597A
Figure 41 Rainbow wood pattern produced by a joint treatment with fungal species 401A +
706B + 597A
40 of 50
Figure 42 Rainbow wood pattern produced also by a joint treatment with fungal species 401A
+ 706B + 597A
Figure 43 Rainbow wood pattern produced by a joint treatment with 8 fungal species
6.2
Decolorizing wood stain with bleaching fungal species
Among the 20 fungal species tested, 17 species were able to decolorize at least one type of stains from
wood of white pine, sugar maple and yellow birch (Table 14). Among these fungi, 6 species (392A,
105A, 815A, 897A, 569A and 82C) were capable of decolorizing 1 type of stain; 6 species (857A, 284A,
71A, 523C, 718B and 473C) were capable for 2 types of stains; 3 species (52A, 480A and 323A) were
capable for 3 types of stains; and 2 species (75A and 345A) were capable for all 4 types of stains tested.
Two values in the mathematical equation of the color metric difference described in section 5.1.3 are able
to quantify the degree of decolorized wood by a particular fungal species; ∆E* represents the general
color metric difference and ∆L* represents the lightness difference before and after treatment. For an
effective treatment to decolorize wood stain, the ∆E* value should be higher than 6 (high color
difference) and the ∆L* value should be lower than -6 (high lightness difference). Among the selected
fungi, 10 species were able to decolorize white pine blue stain at ∆E* values between 16.23 and 21.48
and ∆L* values between -7.21 and -21.23, 4 species were able to decolorize white pine coffee stain at
∆E* values between 11.64 and 13.03 and ∆L* values between -10.29 and -12.06, 10 species were able to
decolorize sugar maple stains at ∆E* values between 12.6 and 33.91 and ∆L* values between -7.28 and 33.45, and 11 species were able to decolorize yellow birch stains at ∆E* values between 13.22 and 22.9
and ∆L* values between -9.74 and -21.58 (Table 15, Figures 44-47).
41 of 50
Evaluation of effectiveness for decolorized wood samples by selected fungi was not only measured by a
colorimeter, but also visually inspected. Based on both visual and colorimeter evaluations on color
uniformity and lightness of wood samples, 3 fungal species were identified as promising for decolorizing
white pine blue stain, 1 species for white pine coffee stain, 4 species for sugar maple stains and 4 species
for yellow birch stains (Table 16, Figures 48-52).
Table 14 Fungal species with capacity of decolorizing wood stains
Fungal name
Bjerkandera adusta
Fungal code
392A
75A
Coriolus versicolor
Lentinus edodes
105A
857A
Merulius tremellosus
52A
Ophiostoma tetropii
Phanerochaete chrysosporium
815A
284A
Phlebia radiata
345A
Phlebiopsis gigantea
Pleurotus ostreatus
897A
71A
Pleurotus ulmarius
Polyporus dichrous
569A
480A
Poria subvermispora
323A
Poria obliqua
523C
Pycnoporus cinnabarinus
Sporothrix sp.
82C
718B
Trogia crispa
473C
Wood species
White pine
Sugar maple
Yellow birch
White pine
White pine
White pine
Yellow birch
White pine
Sugar maple
Yellow birch
White pine
Sugar maple
Yellow birch
White pine
Sugar maple
Yellow birch
White pine
White pine
White pine
Sugar maple
Yellow birch
Yellow birch
Sugar maple
Yellow birch
White pine
Yellow birch
White pine
White pine
Sugar maple
Yellow birch
Sugar maple
Sugar maple
Yellow birch
Sugar maple
White pine
Stain type
Blue stain
Multiple stains
Multiple stains
Coffee stain
Blue stain
Coffee stain
Multiple stains
Blue stain
Multiple stains
Multiple stains
Blue stain
Multiple stains
Multiple stains
Blue stain
Multiple stains
Multiple stains
Coffee stain
Blue stain
Blue stain
Multiple stains
Multiple stains
Multiple stains
Multiple stains
Multiple stains
Blue stain
Multiple stains
Coffee stain
Blue stain
Multiple stains
Multiple stains
Multiple stains
Multiple stains
Multiple stains
Multiple stains
Blue stain
42 of 50
Table 15 Decolorization of wood stains by various fungi
Wood species
Stain type
Fungal name
Fungal code
∆L
∆a
∆b
White pine
Blue stain
Bjerkandera adusta
Lentinus edodes
Phlebia radiata
Phlebiopsis gigantea
Polyporus dichrous
Poria subvermispora
Trogia crispa
392A
75A
857A
52A
284A
345A
897A
480A
323A
473C
-18,45
-13,14
-15,47
-11,48
-10,83
-7,21
-21,23
-16,60
-8,43
-20,08
1,56
6,11
6,27
8,28
4,81
4,08
2,87
-0,80
10,68
1,46
3,51
12,99
11,85
15,99
13,06
13,96
1,59
-3,37
14,03
1,87
18,85
19,46
20,47
21,35
17,63
16,23
21,48
16,96
19,54
20,22
Coffee stain
Bjerkandera adusta
Coriolus versicolor
Poria subvermispora
75A
105A
345A
323A
-11,02
-12,06
-10,39
-10,29
2,70
2,53
3,80
6,80
-6,27
-4,24
-3,63
-0,47
12,96
13,03
11,64
12,34
Phlebia radiata
∆E****
Sugar maple
Multiple stains
Bjerkandera adusta
Ophiostoma tetropii
Phlebia radiata
Pleurotus ostreatus
Polyporus dichrous
Poria obliqua
Sporothrix sp.
Trogia crispa
75A
52A
815A
345A
71A
480A
523C
82C
718B
473C
-11,42
-7,28
-21,69
-9,51
-20,89
-24,13
-33,45
-17,01
-26,15
-28,80
3,21
3,44
6,05
2,01
4,50
5,09
4,62
6,13
2,77
10,41
11,42
13,28
5,73
8,02
7,78
3,94
3,10
9,65
2,11
5,42
16,47
15,53
23,24
12,60
22,74
24,97
33,91
20,49
26,38
31,10
Yellow birch
Multiple stains
Bjerkandera adusta
Lentinus edodes
Phlebia radiata
Pleurotus ostreatus
Pleurotus ulmarius
Polyporus dichrous
Poria subvermispora
Poria obliqua
75A
857A
52A
284A
345A
71A
569A
480A
323A
523C
-11,13
-15,47
-9,74
-9,98
-16,45
-20,89
-15,45
-17,31
-15,01
-21,58
2,92
6,27
0,13
3,18
3,75
4,50
0,74
0,47
2,01
5,27
10,93
11,85
13,93
8,29
12,24
7,78
-1,68
-3,19
8,10
5,57
15,87
20,47
17,00
13,36
20,84
22,74
15,56
17,61
17,17
22,90
Sporothrix sp.
718B
-13,11
1,57
0,57
13,22
43 of 50
Table 16 Most promising fungi for decolorizing wood stains by visual evaluation
Wood species
Stain type
Fungal name
Fungal code
∆L
∆a
∆b
White pine
Blue stain
Phlebia radiata
52A
345A
Trogia crispa
Coffee stain
Phlebia radiata
Sugar maple
Multiple stains
Bjerkandera adusta
Phlebia radiata
Yellow birch
Multiple stains
Pleurotus ostreatus
∆E****
-11,48
-7,21
8,28
4,08
15,99
13,96
21,35
16,23
473C
-20,08
1,46
1,87
20,22
345A
-10,39
3,80
-3,63
11,64
75A
345A
82C
-11,42
-9,51
-17,01
3,21
2,01
6,13
11,42
8,02
9,65
16,47
12,60
20,49
Trogia crispa
473C
-28,80
10,41
5,42
31,10
Phlebia radiata
52A
345A
284A
-9,74
-16,45
-9,98
0,13
3,75
3,18
13,93
12,24
8,29
17,00
20,84
13,36
71A
-20,89
4,50
7,78
22,74
Lightness of white pine blue stain after treatment with various
fungi
0
392A
75A
857A
52A
284A
345A
897A
480A
323A
473C
-5
∆L*
-10
-15
-20
-25
Fungal species
Figure 44 Decolorization of white pine blue stain by various fungi
44 of 50
Lightness of white pine coffee stain after treatment with various
fungi
0
75A
105A
345A
323A
∆L*
-5
-10
-15
Fungal species
Figure 45 Decolorization of white pine coffee stain by various fungi
Lightness of sugar maple stain after treatment with various
fungi
0
75A
52A
815A
345A
71A
480A
523C
82C
718B
473C
-5
-10
∆L*
-15
-20
-25
-30
-35
Fungal species
Figure 46 Decolorization of sugar maple stains by various fungi
45 of 50
Lightness of yellow birch stain after treatment with various
fungi
0
75A
857A
52A
284A
345A
71A
569A
480A
323A
523C
718B
-5
∆L*
-10
-15
-20
-25
Fungal species
Figure 47 Decolorization of yellow birch stains by various fungi
Figure 48 Decolorized (lower part) blue stain and coffee stain on white pine wood samples by
Trogia crispa (473C, left) and Phlebia radiata (345A, right), respectively
46 of 50
Figure 49 Decolorized (lower part) sugar maple stains by Bjerkandera adusta (75A, left) and
Trogia crispa (473C, right), respectively
Figure 50 Decolorized (lower part) yellow birch stains by Merulius tremellosus (52A, left),
Phanerochaete chrysosporium (284A, middle) and Pleurotus ostreatus (71A, right),
respectively
47 of 50
Figure 51 Uniformly decolorized sugar maple stained wood samples by the fungus
Bjerkandera adusta (75A)
Figure 52 Non-uniformly decolorized sugar maple stained wood samples by the fungus
Phlebia radiata (345A)
48 of 50
7
Discussion
This project demonstrates promising results on coloring wood into various colors and patterns, as well as
decolorizing unpleasant wood colors via biotechnology under laboratory conditions. However, to make
this technology successful for commercial application, the following criteria and problems have to be
solved:
1. Industrial production process to control wood contamination from other micro-organisms. The
wood samples used in the tests of coloring and decolorizing in this project were steam sterilized
before the treatment. We also tested on non-sterilized wood samples; however, the coloring quality
was low for certain colors, such as red and purple, caused by contamination from other microorganisms that had already colonized wood. For industry application, the lumber used should be fresh
and sterilized to control molds or other contaminations.
2. Penetration depth and treatment time with different size of lumber. Many fungal species tested in
this project are able to penetrate into wood for coloring or decolorizing wood fibres and are most
promising for a future commercial application. However, the speed of penetration depends on fungal
species, wood size and incubation conditions such as temperature and relative humidity. For industry
application of the biotechnology developed in this project, control of penetration depth in different
size of lumber within an acceptable incubation period is a key issue for commercialization.
3. Uniformity, intensity and repeatability with different batches of treatment process and wood
resource. The uniformity and intensity of wood colors produced by the biotechnology developed in
this project are key issues for quality control of the products. For industry application of this
technology, lumber may come from trees with various ages and locations, and wood materials used
for treatment may be from different between batches, thus controlling product quality and
repeatability has to be solved before commercialization.
8
Conclusions
For coloring wood via biotechnology:
• 15 fungal species are promising to color wood of sugar maple, white birch and yellow birch into red,
brown, green, grey, black and purple.
• Heartwood was equally stained as sapwood with most fungal species.
• Application of 3 or more fungal species together on wood produced rainbow wood patterns with multiple
colors.
• The process for coloring wood required 1-4 weeks.
• Weathering gradually reduced color intensity.
For decolorizing unpleasant wood stains via biotechnology:
• 17 fungal species are capable of decolorizing unpleasant wood stains: 10 fungal species for white pine
blue stain, 3 species for white pine coffee stain, 10 species for sugar maple stains and 11 species for
yellow birch stains.
• Based on visual and instrument evaluation for color intensity and uniformity of decolorized wood samples,
3 fungal species have been identified as promising for decolorizing white pine blue stain, 1 species for
white pine coffee stain, 4 species for sugar maple stains and 4 species for yellow birch stains.
• The process for decolorizing stained wood required 2-8 weeks.
49 of 50
9
Recommendations
Based on the results of different tests conducted in this project and the problems mentioned above in the
Discussion section for transferring these technologies into commercial products, the following
recommendations should be addressed:



Create a Phase II project for large-scale tests on full-length lumber to address problems mentioned
above.
Decolorizing unpleasant wood colors with fungi was long (up to 8 weeks) and such technology may
be difficult to be realized at an industry scale. Further work is required to identify and purify
bleaching enzymes from the selected fungal species. The treatment of stained lumber with purified
enzymes may reduce treatment time from several weeks, as required by the biotechnology developed
in this project, to several hours in the future.
The potential market and products using these biotechnologies should be identified and the benefits
from increasing product value with these technologies should be analyzed.
10 References
Beggs, T.S. et al. 2001. Bleaching enzymes. U.S. Patent 6218350 B1.
Forest Products Laboratory. 2002. Blue stain. Techline. Issue II-2, 05/02. Madison, WI, USA.
Billmeyer, F.W. and M. Saltzmann. 1981. Principles of color Technology. 2nd Ed. John Wiley and Sons
Inc., NY. 240 pp.
Forest Products Laboratory. 2004. Producing spalted wood. Techline. Issue MO-1, 03/04. Madison, WI,
USA.
Haeghen, Y.V., J.M. Naeyaert, I. Lemahieu and W. Phillips. 2000. An imaging system with calibrated
color image acquisition for use in dermatology. IEEE Transactions on Medical Imaging. 19(7):72230.
Okino, E.Y.A. et al. 2009. Color variation of rubberwood clones and cypress infected by Gloeophyllum
striatum and Phanerochaete chrysosporium. International Biodeterioration and Biodegradation
63(1):41-45.
Robinson, S.C., D.L. Richter and P.E. Laks. 2007. Colonization of sugar maple by spalting fungi. Forest
Products Journal 57(4):24-32.
Rodolfo, C., T. Livio and A. Ottaviano. 2007. White beech: a trichy problem in the drying process.
ISCHP’07. p.135-140.
Schanel, L. 2005. Formation of red pigment during wood decay caused by white-rot fungi. Cellular and
Molecular Life Sciences 22 (8): 517-518
Yang, D.-Q. 2001. Staining ability of various sapstaining fungi on jack pine short log sections. Forest
Products Journal 51 (2):1-4.
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