This is the October 2015 issue of the Carving and Tool Tips section.
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How to prevent your pyrographic art from fading
As many pyrographers know, UV will cause their artwork to fade. While this effect is true, UV is not the actual "direct" cause, but rather acts as a catalyst. Once you know the actual mechanism, you can now prevent it from happening. I have told this story to many customers over the last dozen years, so bear with me....
I had come across a discussion years ago, that took place on a popular pyrograhic list server I had frequented, about pyrography fading, and what could done to prevent it. During the discussion, someone mentioned that when ever she used translucent oil color pencils on her burnings, they tended not to fade or fade as much as they did without it being applied. Also, people had noticed that other materials either didn't fade (like Tauga nuts) or faded slower than basswood (like really dense woods). Most everyone dismissed her observations, and agreed that the pigmentation of the pencils was most likely blocking the UV, hence reducing the fading effects. For some reason, I felt that conclusion was wrong.
I then thought about how it could be that an electromagnetic wave/particle could be causing something that should inherently be chemical in nature. It was a bit of a puzzle, and that bugged me, but I had no immediate answers. So I filed it away in the back of my mind as something to think about or ponder.
While doing something unrelated a few weeks later, the realization of what was happening to cause pyrography to fade hit me like the preverbal ton-o-bricks. A quick call to a local carpenter confirmed my suspicions, and a quick google search about how ozone is created nailed down my now "working theory".
Okay, first you have to know what wood is made out of.... Basically, it is made up of cellulose, water, and air. Even kiln dried wood has a little bit of water in it. The amount of air in a given wood is determined by the density of its cellulose, and so on. Air is basically made up of mostly nitrogen and about 21% oxygen, known to chemists as O2. Now here comes the science. UV, UV-A in particular, has just enough energy to knock electrons on and off of atoms and molecules. How UV fades wood is indirect, in that what it does is that it turns O2 into O3. O3 is known as a radical isotope of oxygen that is very unstable. This instability lends its use in industrial and commercial applications as a disinfectant and a bleach. In fact, it is even more effective at bleaching then chlorine is.
So now that we know that the UV is turning the O2 inside the wood into O3 which reacts with the pyrography burnt onto/into the wood, what can we do about it. Well, the call to the local carpenter was to ask what he would do "exactly" if I wanted to leave the wood around my windows in its "natural" color instead of staining it. His answer was to put down a coat of "clear stain", otherwise known as a clear finishing oil, and then put several coats of polyurethane after it had properly dried. If the carpenter didn't put down the oil first, within a few years the wood would erupt through the polyurethane oxidized and destroyed.
The answer is to use an oil finish to hydraulically displace the oxygen in the wood pores. Over time oil might yellow, but at least it doesn't bleach the wood like oxygen can. The only problem with an oil finish, is that it can darken the wood significantly, which many pyrographers don't like. Most finishing oils are linseed based, which will definitely darken wood grain. But there may be alternatives to linseed oil. I myself have tried mink oil (yep, from real minks) that is normally used on leather on a piece of basswood side grain, and I noticed very little darkening of the wood.
The next step is for someone to develop an oil based product specifically made for this use, that does not darken the wood grain.
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