About Spalted Wood and Burl
The spalting that we find so attractive is the visible changes to the wood resulting
from fungal attack which is part of the natural decay process. Individual spalting
patterns on a specific piece of wood are unpredictable.
There are many variables affecting the process. These include wood species,
temperature, humidity, pH, adjacent soil types, fungus spores in the local
environment, and probably many other variables I haven't identified. Many times only
a small portion of a log will have usable spalting. The remainder may simply decay
without developing a spalt pattern.
Many types of wood will spalt. Some such as maple and birch are known for a more
attractive spalting appearance and remain usable further into the spalting (decay)
Looking for spalted wood is like going on a treasure hunt. After a long walk thru
the woods I may end the day empty handed or find one beautifully spalted dead log
that will keep me busy for weeks.
It is possible to make your own spalted wood, but it also can be an expensive and
time consuming way to turn expensive lumber into humus!
Burls are fast growing abnormal growths on a tree. This is caused by environmental
stress, damage, or disease (fungal or insect attack) on a tree. The rate of
occurrence is usually very low. I have found that the percentage of trees with burl
varies by species and location.
Pictured to the right are two decent sized burls on a 12" diameter wild cherry tree. This
tree appears relatively healthy and will probably live many more years.
The Aspen burl pictured above weighed over 200 lbs (20 inch diameter on a 10 inch
diameter trunk). I found it on a storm downed tree only a few hundred yards from
our house. The cut angle of the half section does not show the full beauty of the
burl which will be revealed as the burl is sectioned. This is the largest aspen burl
I have seen, and there are tens of thousands of aspen within a mile radius of our
Some burls are regular growth rings growing at an accelerated rate. These types
aren't as interesting to look at and aren't as widely known.
The type of burl preferred by most woodworkers is the type that grows in wild
irregular swirling patterns with "eyes". These are particularly noticeable in
some of the closeup pictures of cherry burl on the picture page. The irregular
swirling growth habits of burl that makes it so beautiful also makes it unstable
and difficult to work.
Burls vary in size from a few ounces to several tons. In Northern Wisconsin a burl
over 150 lbs is exceptional.
We obtain our Burls from dying trees and local loggers. Burls don't appear to do a
very good job of passing nutrients to the tree. My experience is that once a burl
completely girdles a tree trunk the tree will die.
Spalted woods may have soft spots that are too far along in the decomposition
process to be workable. The unpredictable shrinking warping and cracking in burl
is due to variations in density and lack of regular grain pattern. For that reason
both these woods are often stabilized to retain the natural beauty while imparting
good physical properties to the material.