Woodworking 101 - Photo-Reactive Woods

Many species of wood offer trully spectacular displays of color and renew our wonder at what beauty can be found in nature. Many of these are affected by light, often the ultra violet portion in particular. I work with a few common to my area I would like to tell you about: Box Elder, Mulberry, Osage Orange, and Cedar. Box Elder Vase

Box Elder is a maple that typically is an uninteresting wood with light heart and sapwood. It often has areas with grayish streaks and overtones, and occassionally red. Once in a while it exhibits absolutely astounding flame red patterns. Unlike the dark colorations in maple caused by the ambrosia beetle, I had believed this brilliant color was the result of the tree's chemical growing environment, but I've been given cause to doubt myself. Whatever the cause, the intense red fades to dull brown when exposed to bright light.

What does cause that spectacular color? I thought I knew, but started hearing a lot of other opinions that seemed to be backed up rather credibly. That said, here is one synopsis of one study and a reference to the erudite article from which it was taken.

Morse, A. C., and Blanchette, R. A. 2002. Etiology of Red Stain in Boxelder. Online. Plant Health Progress doi:10.1094/PHP-2002-0917-01-RS.

The stain’s ubiquitous presence in all wounded tissue and the inability of F. solani isolates obtained from boxelder to stain boxelder red in wood block studies indicates that red stain is most likely produced by the tree as a nonspecific host response to wounding.

You may read the article at http://www.plantmanagementnetwork.org/pub/php/research/redstain/.

Cedar has beautiful burgundy red heartwood with creamy light heartwood when freshly cut, but (You guessed it!) turns dull brown when left Eastern Red Cedar

exposed to the elements. However, I have it from a usually reliable source that it is not light, but good ol' O₂ you and I need to breath, that is the culprit. The reactive chemicals in the heartwood that make it so resistent to weather and bugs also react with the oxygen in the air. That's why that wonderful cedar aroma from the block you have hanging in the closet goes away after some time. To get it back you need only sand the block a bit to expose the underlying layers where the reactives are still fresh.

When I finish a piece of cedar I can have brilliant color or a wonderfuI aroma, but I must choose one or the other. I still tell my customers to keep it out of that south facing window in the summertime. (See my disclaimer.)

These are certainly not the only species of wood that change color under the influence of their environment. They are only some of the more common species I work with, and I present this to help people enjoy my work for a lifetime and longer.

Mulberry and Osage Orange are, to me, very similar. They are both very dense with with wonderful golden yellow-orange heartwood with contrasting lighter sapwood. Left in the sun, both grow dull and brown.

Disclaimer. Please understand what you find here is not the result of an extensive scientific literature review but rather my own version to help the average person unfamiliar with wood keep from destroying the very thing that may have motivated them to purchase a nice piece of turned wood. Further, in the case of cedar, photo-reactivity may play a minor role relative to the oxidation process that occurs. In any case, I will be please to include any corrections I come upon or any authoritative corrections you may wish to submit.

Copyright 2007 Eric Urban All rights reserved.