Turning Archive

Definitive fade test
Response To:
Re: Box Elder fade test ()

John K Jordan
>>>I'm wondering about oxidation. Flipping the board shields the lower face from light, and also the air. Does that also contribute to the difference?

That question has been asked over the years. I've read many opinions and anecdotal "evidence" but I have never seen any definitive answer. Usually the speculation is that both UV light and oxidation contribute to the color change.

Perhaps someone has done and published the research somewhere but I have not yet found it. Anyone have time for an experiment? This could be done in Colorado springs.

This kind of test could provide be excellent data for a magazine article and to let online reference people, like the guy who runs the Wood Database, refine their articles. Wood collectors, museums, and wood art collectors might also be interested.

A literature search for existing research might save a lot of effort! If no existing research is found, it might be possible to get some wood science doctoral student interested. That would be a lot easier too.

I propose putting samples of boxelder and other species known to change color (purple heart, boxelder, padauk, ??) in various containers to control the environments. Needed: containers that can be sealed, inert gas, UV light sources, and ideally, an optical device to read color. For dark conditions the containers could be light proof or several containers could be placed in a dark environment. For UV light conditions, non-UV absorbing containers could be stored in a chamber with a single UV light.

Cut all samples of each species from the same typical board with even coloring. Since differences in individual growth environments may contribute, a better test would include samples from several different trees.

1 - samples in inert gas in UV light.
2 - with oxygen and UV light
3 - with oxygen in the dark

1 - control 1: with inert gas in the dark
2 - (casual): hang samples on a wire in a "typical" indoor environment, out of any sunlight from a window.
3 - (casual): same as Control 2 but near a window that gets some sunlight.

Two basic assumptions: that light from the UV part of the spectrum and the oxygen component of air are the primary contributors to fading. Another set of conditions using controlled wide spectrum light and atmospheric air would be useful. Other variables to complicate things or for additional research: temperature, pressure, various common finishes (UV inhibitors, etc.), other?

Measure each sample with a colorometer on freshly cut surfaces before the tests. Take multiple color samples on each piece and mark the locations of each. Measure again after waiting some arbitrary time. For better data, put the samples back in the test environments and periodically repeat the color measurement.

Possible complications: some wood initially changes then seems stable for some time before degrading. For example, some purple heart is brown when first cut, then turns purple after a few days of exposure? Perhaps the initial color test interval could be short enough to accommodate the typical initial ph brown-to-purple change. To add to the effort, I have a carefully guarded and dwindling supply of other purple heart which is a beautiful purple immediately when cut and stays purple much longer. (I was told it came from Mexico, but I don't know if that's a fact since I didn't harvest it.) A definitive test should include samples of this specific wood and possibly others with varieties with known or suspected differences. Another example: Lissi Oland gave me some box elder cut from the root ball of a tree - the red was far deeper and my subjective impression was the color lasted longer, perhaps due to the more intense initial color. Don't know.


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