Here is a photo of a piece of Box Elder I have had on my tool chest for the last year. The piece on the right was always face down and never got any sunlight. The piece on the left was flipped over every time I walked in the shop so each side got 1/2 a year of non direct sunlight. In a previous test I did Box Elder in direct sunlight would fade in just 3 days. I could not capture the actual fade in a photograph. The one on the right is brighter. The one on the left has lost a fair amount of color and the yellow darkened.
No it's losing its color, just very slowly. that piece was simply sawed in half so both halves should have looked the same but the left one when viewed in person is definitely softer in color. If you put a UV finish on I would say after a year there would be very little change. Maybe after 10 years a pretty fair change. That's the difference between not ever putting a piece in direct sunlight but still displaying it in your house.
I don't think that there is any doubt that Box Elder will fade in sunlight. But kept away from bright sunlight it does last a long time. That is why I use red Trans Tint Dye on Box Elder to make sure it stays red.
Although it addresses exotics, it also applies to box elder. In general, give up. If you want color, use dye.
That said, I have a dwindling supply of enchanted Purple Heart. Unlike most, it is purple when cut into and stays purple. The wood had been stored for decades inside but still with plenty of light and the outside surfaces were purple. I made some things from it that are still a rich purple after about four years. I was told it is a variety from Mexico. I'd like to find some more.
Perhaps there is a magic variety of box elder out there somewhere.
>>>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
CONTROLS
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.
Perhaps 10 years ago I spent an hour on the internet reading everything I could find on red box elder. One find was a research paper that concluded after a series of experiments that the red color was due to injury or other insult to the wood and not to fungi. I also found a comment that a woodturner had asked his neighbor research chemist to analyze the red color. The chemist said it was a type of relatively unstable molecule that would be degraded by UV light. A quick search just now did not find the research paper or the comment.
One of my good friends turned a lot of box elder. He said you won't find the red in a tree back in the woods. It's almost always innate tree near a barn or power lines. He felt that if the tree is in a stressed environment that it will get the color. That pretty much goes along with that first paper.
(which is still on the Internet on 11/11/2018) and the mention of a chemical analysis of the red color was in a forum on turned wooden pens (did not note the forum name or the citation) but the chemistry professor neighbor found the red color to be a phenol compound that would be modified to a brown color by the energy in sunlight. It would seem likely that the energy in artificial light would have the same effect, dependent on the relative amount of energy in sunlight and artificial light.
