Figuring out figure—spalt
Spalting is a figure pattern caused by fungus growing in trees and logs. It produces black streaks usually growing with the grain and can result in a beautiful marbling (image 1). Some species are more prone to spalting such as maple, birch and beech, while others such as walnut rarely spalt. The fungus enters the tree through an injury and starts to spread. The trick is to get dense spalting before the lumber turns to punk. It is not uncommon to find a log with spalting penetrating the end grain for a short distance but this can be little more than a distraction. What every woodworker wants is a spalted board where the black lines weave over the face like a spider web. This is enhanced when combined with other figure patterns such as burl (image 2) or birds eye (image 3).
Some individuals have been able to get logs to spalt by storing them in a fungus-prone environment. We have had mixed results trying some of these methods, one time getting good spalt and the next time a rotten log.
Respirators are essential when working with spalt in that it is a fungus that can grow in your lungs. Keep your work area clean at all times and be careful where and how you dispose of the dust.
About the author: Rick Hearne, owner of Hearne Hardwoods Inc. in Oxford, Pennsylvania, has been in the specialty lumber business for more than 25 years. Hearne Hardwoods carries an inventory of 1 million board feet of lumber in 120 different species, including at least 100,000 board feet of variously figured maple.