What is Chatoyance?

Chatoyance comes from a French word meaning 'Cat's Eye'.  It is the optical illusion you see in certain polished woods or gems that give it a hologram effect.  When wood is described as having 'figure', this is a type of chatoyance.  Type's of 'figure' are flame, quilted, tiger stripe, cat's eye, or ribbon. 

Pieces of wood with chatoyance are more rare and interesting, so are sought after by wood workers and admired by collectors. 

As the tree grows, stresses are applied to the trunk causing some portions of the grain to very tight and some loose. These tight and loose grains can manifest as lines, circles, or random patterns.  Applying certain types of finishes (or even water) bring out this effect as the different alternating grains absorb the finish at different rates, reflecting more or less light. This variance in reflectivity, or more exactly, when light scattering no longer occurs, is what causes the optical illusion of depth and creates the patterns that we see.