Wood and natural aging
One of my entries took a blue ribbon at the Lines into Shapes art show in Estes Park, Colorado, in November. It was a real honor to win an award in a show with so many entries from around the country, and I am proud of the little pot that won the sculptures division. I had made this piece –an apple pot with walnut and figured maple inserts- in the spring of 2012, and as the judge held it high during the awards ceremony I couldn’t help noticing that the maple insert ring had yellowed in two years’ time.
The truth is, all wood darkens with age. Light woods such as holly, pine, and maple tend to yellow. Exotic woods like purpleheart and padauk slowly fade to brown. Cherry darkens even in the first few days after being worked, and continues to darken for up to a century according to some sources.
All three cutting boards in the photo are made of cherry: in the rear is one about 9 months old; the others are three days old and differ only in that the one in the center has been oiled. The difference is striking. The cherry in a cutting board I gave my mom about five years ago is now almost as dark as the walnut that accompanies it.
Why does this happen? We’d need an understanding of polymer chemistry to fully understand the process. Basically, polymerization of polyphenols causes darkening as tannins are produced. UV light seems to be the catalyst. I’m not much of a chemist but I know that wood darkens. Finishes won’t stop this process from happening, not even spar varnishes loaded with flattening agents.
This means two things to a woodworking artist. First, natural darkening in wood isn’t a bad thing, just a thing that needs to be accounted for. When combining multiple woods into one piece of artwork, we must consider how each species will look in the future so that colors don’t lose the contrasts that made them attractive in the first place. And most importantly, because wood colors eventually do darken, it is the shape of an object that ultimately determine its worth generations from now. I believe it is for this reason that the best wood turners alive today emphasize shape and form in turned art work.