Spalting occurs when certain types of fungi, called decay fungi, attack and discolor a tree's wood. Many people find the discoloration patterns spalting produces attractive and a market exists for products made from "spalted" wood. Spalting represents the early stages of decay and typically causes a noticeable softening of the affected wood.
Certain conditions must exist before spalting can take place. Temperatures between 70 to 90 degrees Fahrenheit provide the optimal climate for spalting. Also, some species of trees have a higher susceptibility to spalting than others. Generally, hardwoods have a higher vulnerability than softwoods. Hardwoods with a low decay resistance, such as maple, beech and birch frequently spalt, according to the Ohio Department of Natural Resources. The rate at which wood spalts varies, depending on the species and climate conditions.
White rot fungi, various species of fungi that primarily attack hardwoods, cause a bleaching effect on the the host wood. Typically, this occurs because the fungi reduce the amount of lignin, a pigmented chemical in the tree. White rot tends to decay the affected wood more slowly than other types of fungi. However, even though the decay process happens slowly, white rot, given enough time, can still cause enough strength loss to ultimately make the wood unusable.
A specific type of spalting discoloration, called zone lines, results in dark lines running through the wood. The cause of zone lines is under debate by the scientific community. The most commonly accepted theory is that zone lines occur when two competing species of fungi meet in a contested portion of wood. Zone lines represent a fungi's attempt to protect its feeding area from another species, according to "Colonization of Sugar Maple by Spalting Fungi," published in the April 1, 2007 issue of "Forestry Products Journal."
Many artists and craftsman place a high value on spalted wood for the unique beauty of each individual piece. No two pieces of wood have the exact same appearance, which makes the material particular appealing. Those working with the wood must find the piece at the right time of the spalting process. If you find a piece of wood too early, it might not have attained a compelling appearance. If you get the wood too late, it might have decayed to far to work. Some craftsman induce spalting under artificial conditions, with inconsistent results.