You may not know the term “chatoyance”, but you’ve probably seen it. The term derives from the French word “chatoyer”, which means “to shine like a cat’s eye.” If you’ve ever seen a the semi-precious stone tiger's eye, you get the idea. In woodworking, chatoyance is a similarly striking optical quality in which areas of light and dark grain shift and change position depending on the angle of view. The effect is most pronounced in burls and other wavy-grained woods, where abrupt changes in grain direction cause the concentration of reflected light to change dramatically based on the orientation of the surface of groups of wood cells.
Chatoyance is most often considered a desirable effect, and can be enhanced or diminished during the finishing process. There are any number of recipes for maximizing the chatoyance of a finished piece of wood. Most call for a dye stain or other translucent colorant – as apposed to a pigmented stain - and an oil or shellac finish. Here’s one offered by finishing expert Michael Dresdner in answer to a question on producing a tiger eye finish on quilted maple:
“…Tiger eye is brown and gold, with loads of chatoyance. To do that on quilted maple, start with a dilute dark brown water soluble dye (van dyke brown will do nicely.) Flood it liberally onto the wood and wipe it off immediately. Although it is a dark color, a dilute or weak dye will mostly color endgrain. Let the wood dry. Then re-sand it with 220 grit paper to remove the dye from any flat grain surfaces. You'll find that leaves plenty of color in the pores, accentuating the figure. Now re-stain with a honey amber dye mixed to whatever color and intensity you prefer for the contrast color. This will tint the flat areas in between the dark figure lines, and you will have a tiger eye look complete with flip flop as you look at it from different angles. Top it off with a finish that accentuates the depth in wood -- shellac, lacquer, or oil."
From the Woodworker's Journal eZine archives
Sometimes, chatoyance is a nuisance. Veneers in some species will produce a striking and unwanted contrast at the intersection of two bookmatched flitches. In that case, minimizing chatoyance is the desired effect. Again, there are various opinions on the best way to achieve this. In general, the goal is to minimize the amount of light that makes it to the surface or the offending wood cells and straight back out to the viewer’s eye. Pigmented stains and toners in the top coat are generally the recommended course of action.
There are, of course, other factors involved, including the way the veneer is cut, and the fact that many woods that exhibit a high degree of chatoyance are also very difficult to stain evenly with pigmented stain. “Lightness Variations in Bookmatched Veneers Panels” from the Woodweb Knowledge Base offers a good basic overview of the situation along with a couple of possible solutions. For an all-around education on the sometimes surprising relationships between wood, wood finish and light, we recommend a wood finishing book, like Jeff Jewitt's Great Wood Finishes or Michael Dresdner's The New Wood Finishing Book, and lots of experimentation.