Q. We are seeing erratic coloring in our oak when finishing with stains. We also recently have seen this fuming too. Will all the wood from one log have the same color behavior? What causes this stark variation?
A. One of the beauties of wood is its variation in color. I suspect that in your case that you are seeing color variation due to a variation in the basic cellular structure in the wood.
When a tree is put under stress (wind blowing from the same direction, struggling for sunlight due to shade from another tree, one tree leaning against another, heavy branch, etc.), the hardwood tree reacts by forming tension wood cells, rather than the standard or “normal” cell.
The tension wood cell typically has much more cellulose (cotton is cellulose) and less lignin (the glue and stiffener chemical). So, tension wood cells are very absorptive of stains and will behave differently when heated.
Tension wood is often spread over a wide area of the wood in a tree stem. So, we will see variations from tree to tree, as well as within an individual tree.
Having said this, we also know that color variations occur due to soil variation, species differences (there are thirty commercial species of oak that are sold as red and white oak), growth rate, kiln temperatures, and more.