Spalting

Spalting is any form of wood coloration caused by fungi. Although primarily found in dead trees, spalting can also occur in living trees under stress. Although spalting can cause weight loss and strength loss in the wood, the unique coloration and patterns of spalted wood are sought by woodworkers. Spalting is any form of wood coloration caused by fungi. Although primarily found in dead trees, spalting can also occur in living trees under stress. Although spalting can cause weight loss and strength loss in the wood, the unique coloration and patterns of spalted wood are sought by woodworkers. Spalting is divided into three main types: pigmentation, white rot and zone lines. Spalted wood may exhibit one or all of these types in varying degrees. Both hardwoods (deciduous) and softwoods (coniferous) can spalt, but zone lines and white rot are more commonly found on hardwoods due to enzymatic differences in white rotting fungi. Brown rots are more common to conifers, although one brown rot, Fistulina hepatica (beefsteak fungus), is known to cause spalting. Pigmentation is caused when fungi produce extracellular pigments inside wood. Bluestain is also a form of pigmentation, however generally bluestain pigments are bound within the hyphae cell walls. A visible color change can be seen if enough hyphae are concentrated in an area. Pigmenting fungi classified as spalting fungi do decay wood, they simply do so at a slower rate (soft rotting) than white rotting fungi. The most common groups of pigmentation fungi are the imperfect fungi and the ascomycetes. Mold fungi, such as Trichoderma spp., are not considered to be spalting fungi, as their hyphae do not colonize the wood internally and they do not produce the enzymes necessary to digest the wood cell wall components. The mottled white pockets and bleaching effect seen in spalted wood is due to white rot fungi. Primarily found on hardwoods, these fungi 'bleach' by consuming lignin, which is the slightly pigmented area of a wood cell wall. Some white rotting can also be caused by an effect similar to pigmentation, in which the white hyphae of a fungus, such as Trametes versicolor (Fr.) Pil., is so concentrated in an area that a visual effect is created. Both strength and weight loss occur with white rot decay, causing the 'punky' area often referred to by woodworkers. Brown rots, the 'unpleasing' type of spalting, do not degrade lignin, thus creating a crumbly, cracked surface which cannot be stabilized. Both types of rot, if uncontrolled, will render wood useless. Dark dotting, winding lines and thin streaks of red, brown and black are known as zone lines. This type of spalting does not occur due to any specific type of fungus, but is instead an interaction zone in which different fungi have erected barriers to protect their resources. They can also be caused by a single fungus delineating itself. The lines are often clumps of hard, dark mycelium, referred to as pseudosclerotial plate formation.