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Spalted wood is colored by fungus living within the structure. The coloring gives the wood a unique appearance and increases its value. While the fungus will also harm the wood, measures may be taken by the woodworker to minimize its impact on the structure. Spalted wood is commonly used for artistic wooden pieces, such as decorative bowls or statues. Although most varieties of spalted wood are safe for human interaction, their weakened state and potential health hazard typically makes them unsuitable for some purposes.
In general, usable spalted wood is only found in hardwoods, like maple, oak and beach. Softwoods, such as pine, have a common fungus called brown rot. This fungus rapidly destroys the wood, making it unusable for woodworking.
Spalting is generally broken down into three areas: pigmentation, white rot and zone lines. Any spalted wood may just have one or all three. The variety of fungus that grew in the tree combined with the conditions that caused the fungus to grow influence the final appearance.
Pigmentation changes are modifications in color that permeate the sapwood of a tree. Sapwood is the more porous outer area of the tree in between the bark and the heartwood. The fungi that cause this change are generally very dark in color, often a deep blue. While pigmentation changes in a tree do not accelerate wood decay, they do make the wood more porous, which makes it more susceptible to damage.
White rot is the hardwood form of brown rot. This creates areas inside the wood that appear bleached; long, thin, ovoid regions that have little to no wood color. This effect is caused when the fungus in the wood eats the part of the wood cell containing the distinctive brown colorations. The fungi that make up white rot will eventually destroy the wood, so steps need to be taken to kill the fungus and seal the area. The softwood brown rot acts the same as white rot, just faster and without the unique pattern.
Zone lines are dark lines that run through the wood. These lines often form an ovoid shape since they mark the edge of a specific fungus’s impact on the wood. As a fungus expands, if it recognizes the presence of other fungi in the wood, it will erect a barrier to protect the area. This creates a dark line of non-permeable material within the wood. While the zone line itself is harmless for the wood, the fungi that make it may not be.