Sara C. Robinson

A Method for Digital Color Analysis of Spalted Wood Using Scion Image Software

Color analysis of spalted wood surfaces requires a non-subjective, repeatable method for determining percent of pigmentation on the wood surface. Previously published methods used human visual perception with a square grid overlay to determine the percent of surface pigmentation. Our new method uses Scion Image©, a graphical software program used for grayscale and color analysis, to separate fungal pigments from the wood background. These human interface processes render the wood block into HSV (hue, saturation, value, within the RGB color space), allowing subtle and drastic color changes to be visualized, selected and analyzed by the software. Analysis with Scion Image© allows for a faster, less subjective, and easily repeatable procedure that is superior to simple human visual perception.

Effects of substrate on laboratory spalting of sugar maple

Abstract Spalting is the coloration of wood caused by fungal colonization. Woodturners, craftspeople, and artists appreciate spalted wood for its aesthetic appeal and uniqueness. Laboratory-induced spalting aims at a repeatable procedure in which wood is inoculated with selected fungi to obtain natural color with high aesthetic appeal, low weight loss and good machinability. Vermiculite (a natural clay with a high capacity for water holding and cation exchange) has been the primary incubation substrate for spalting research despite soil being the standard substrate for soil block decay testing. In this research, we explored the differences between these two substrates and their effects on the growth of spalting fungi on sugar maple (Acer saccharum) wood. Five fungi, Trametes versicolor, Xylaria polymorpha, Arthrographis cuboidea, Ceratocystis pilifera, and Ceratocystis virescens, were tested for their weight loss and spalting abilities on 14-mm sugar maple cubes incubated in both soil and vermiculite. Weight losses from all fungi were either unaffected or reduced by incubation in vermiculite compared to soil. In vermiculite, X. polymorpha produced more zone lines and A. cuboidea produced more pigment than blocks incubated in soil. Growth in vermiculite decreased weight loss of blocks inoculated with T. versicolor and X. polymorpha, while bleaching was unaffected regardless of substrate. External blue stain was higher on blocks inoculated with either Ceratocystis species and incubated in soil. These results indicate that vermiculite is a better substrate for spalting regardless of fungus due to the higher external pigmentation, lower weight loss, and better color contrast on the sugar maple blocks incubated in this substrate.

Wood Colorization through Pressure Treating: The Potential of Extracted Colorants from Spalting Fungi as a Replacement for Woodworkers' Aniline Dyes

The extracellular colorants produced by Chlorociboria aeruginosa, Scytalidium cuboideum, and Scytalidium ganodermophthorum, three commonly utilized spalting fungi, were tested against a standard woodworker’s aniline dye to determine if the fungal colorants could be utilized in an effort to find a naturally occurring replacement for the synthetic dye. Fungal colorants were delivered in two methods within a pressure treater—the first through solubilization of extracted colorants in dichloromethane, and the second via liquid culture consisting of water, malt, and the actively growing fungus. Visual external evaluation of the wood test blocks showed complete surface coloration of all wood species with all colorants, with the exception of the green colorant (xylindein) from C. aeruginosa in liquid culture, which did not produce a visible surface color change. The highest changes in external color came from noble fir, lodgepole pine, port orford cedar and sugar maple with aniline dye, cottonwood with the yellow colorant in liquid culture, lodgepole pine with the red colorant in liquid culture, red alder and Oregon maple with the green colorant in dichloromethane, and sugar maple and port orford cedar with the yellow colorant in dichloromethane. The aniline dye was superior to the fungal colorants in terms of internal coloration, although none of the tested compounds were able to completely visually color the inside of the test blocks.

Utilizing Extracted Fungal Pigments for Wood Spalting: A Comparison of Induced Fungal Pigmentation to Fungal Dyeing

The lengthy time periods required by current spalting methods prohibit the economically viable commercialization of spalted wood on a large scale. This work aimed to compare the effects of induced spalting in 16 Pacific Northwest woods using three common spalting fungi, Chlorociboria aeruginosa, Scytalidium cuboideum, and Scytalidium ganodermophthorum, with the significantly less time-consuming treatment of these woods using dichloromethane-extracted green, red, and yellow pigments from the same fungi. For pigment extracts, the dosage required for a pigment to internally color various wood species to 30% internal coverage was investigated. With few exceptions, treatment with pigment extracts outperformed induced spalting in terms of percent internal color coverage. Cottonwood consistently performed best with all three pigment solutions, although chinkapin performed as well as cottonwood with the red pigment, and Port Orford cedar performed as well with the yellow pigment. While no wood species showed 30% internal color coverage with the green pigment solution, a number of additional species, including pacific silver fir, madrone, dogwood, and mountain hemlock showed internal color coverage on the order of 20–30% for red and/or yellow. Cottonwood was determined to be the best suited wood species for this type of spalting application.

Ability of three yellow pigment producing fungi to colour wood under controlled conditions

Abstract Inonotus hispidus, Scytalidium ganodermophthorum and two strains of Scytalidium lignicola were tested for their ability to produce yellow extracellular pigment on media plates, sterile wood blocks and non-sterile logs to determine their suitability for use as spalting fungi. All three fungi produced a penetrating yellow pigment in the non-sterile logs after 12 weeks of incubation; however, results from the sterile block tests indicated that the incubation time necessary for I. hispidus to produce sufficient yellow pigment may be as low as 4 weeks of incubation. An incubation period of 4 weeks is the shortest recorded for controlled spalting and will allow for the currently utilised production time for yellow spalted wood of 12 weeks to be substantially decreased using an isolate of I. hispidus as the inoculum.

Wood Species and Culture Age Affect Zone Line Production of Xylaria polymorpha

Three pure cultures of Xylaria polymorpha were isolated from fruiting bodies at yearly intervals over two years and maintained on 2% malt agar plates at room temperature. Immediately after isolation of the third culture, the cultures were inoculated onto sugar maple (Acer saccharum), aspen (Populus tremuloides), birch (Betula alleghaniensis), and basswood (Tilia americana) 14 mm cubes and incubated for 10 weeks in jars containing vermiculite. More zone lines were produced on aspen and sugar maple than on yellow birch or basswood. Increasing culture age generally caused a decrease in zone line production; however the effect was only statistically significant in sugar maple. The results indicate that aspen is preferable for zone line production with X. polymorpha, as both external and internal zone lines occur on this wood species, and zone line production remains high despite the age of the culture.

Potential for carrying dyes derived from spalting fungi in natural oils

Wood colored internally by fungi has long been used by woodcrafters and artisans as a substitute for synthetic dyes. Recent advances in the field of spalted wood have led to methods by which the fungal dyes can be extracted from either a fungal solution or colonized wood and then reapplied to clear wood. This takes the “guess work” out of spalting, as well as the time necessary for fungal colonization; however, it requires organic solvents like dichloromethane, which are toxic and not readily available to consumers. Herein, the authors show that the dyes can be successfully carried and blended together (to increase the range of colors) in a range of natural oils. The blue–green dye of Chlorociboria species, called xylindein, carried best in raw linseed oil, the red dye of Scytalidium cuboideum performed best in Danish oil, although more dye could be carried in raw linseed oil, and the yellow dye of Scytalidium ganodermophthorum performed best in walnut oil. The ability to carry and mix these dyes in easily purchased, nontoxic oils opens up their use to woodworkers who seek to follow the traditions of spalted wood, but do not have the skills or time to work with live fungal cultures or fungal dyes suspended in toxic organic solvents.

Methods of inoculating Acer spp., Populus tremuloides , and Fagus grandifolia logs for commercial spalting applications

One of the most promising wood value-added processes currently under development is spalting, where pigment is added to wood via fungal colonization. Previous studies have shown laboratory level spalting to be achievable and highly predictable. However, large-scale spalting for potential commercial applications introduces a substantial number of additional variables which impact the spalting process. To test the potential of commercial-scale spalting, Acer saccharum, Fagus grandifolia, and Populus tremuloides logs were inoculated with multiple known spalting fungi utilizing both liquid spray cultures and live dowel pin cultures. Many of the fungi that successfully produce spalting in small, sterile cultures also produced significant amounts in large logs, with many spalting patterns identical to those found in small-scale testing. Pairings of Trametes versicolor/Scytalidium cuboideum and Xylaria polymorpha/Xylaria polymorpha (different isolates) produced significant amounts of zone lines. In addition, the method of inoculation impacted the amount of spalting: more zone lines were produced when fungi were introduced via plugs, while more stain was produced when liquid cultures were sprayed onto the logs. These results indicate that many of the standard spalting fungi are suitable for large-scale applications; however, the inoculation method appears to be a vital component for successful spalting under a restricted time schedule.

Microscopic Analysis of Pigments Extracted from Spalting Fungi

Pigments that are currently available in the market usually come from synthetic sources, or, if natural, often need mordants to bind to the target substrate. Recent research on the fungal pigment extracts from Scytalidium cuboideum, Scytalidium ganodermophthorum, Chlorociboria aeruginosa, and Chlorociboria aeruginascens have been shown to successfully dye materials, like wood, bamboo, and textiles, however, there is no information about their binding mechanisms. Due to this, a microscopic study was performed to provide information to future manufacturers interested in these pigments. The results of this study show that S. ganodermophthorum and C. aeruginosa form an amorphous layer on substrates, while S. cuboideum forms crystal-like structures. The attachment and morphology indicate that there might be different chemical and physical interactions between the extracted pigments and the materials. This possibility can explain the high resistance of the pigments to UV light and color fastness that makes them competitive against synthetic pigments. These properties make these pigments a viable option for an industry that demands natural pigments with the properties of the synthetic ones.

Microscopic Investigation on Fungal Pigment Formation and its Morphology in Wood Substrates

Melanin formation and assembly by fungi has largely been investigated mainly for its importance in pathogenesis, as well as to establish the functions and biosynthetic pathways of melanin formed during the process of successional wood decay. It is known that melanin formation varies based on fungal species, especially melanin produced by ascomycetes versus basidiomycetes, and that the mechanisms of melanin production by basidiomycetes are more complex and thus far not entirely elucidated. This study compares in vivo melanin formation by Oxyporus populinus in sugar maple and Fomes fomentarius in birch, and in vitro pigmentation by Trametes versicolor, Xylaria polymorpha and Inonotus hispidus in sugar maple and beech, with and without the influence of the melanin precursor, catechol. The results of this research indicate a bi- or multi-modal activity of melanin production and assembly by wood decay fungi, and identify possible variations in melanin formation mechanisms as influenced by fungal and wood species.