Understanding Western PA Cherry Wood...

[Bill Space]

Hi,

I am wondering about the darkening of cherry wood. I don't really have much experience with it...but heard it darkens over time.

I bought some cherry from a friend at work. He cut it on his farm and had it rough sawed. Most I had kiln dried after he had it sitting in his barn air drying for a year or two. Some I have in the air dried state.

So I did a little test. First I took a piece that I surface planed and put a piece of stainless steel that I had handy across the middle of it and put it in a south facing window. I let it sit there for a few months, then remembered it, and took a look. Surprisingly, the area that was shielded from the sun (under the piece of stainless steel sheeting) was quite darker than the wood that was exposed to light and air.

Then this afternoon, I noticed a cut off piece of cherry, that remained from a transition piece that I made to cover the transition between a carpeted floor and a tiled floor. This piece was in the basement shop, which does have a lot of windows, being an above ground basement on two sides, but the piece in question was back away from the windows. The location on the first floor of the house where the transition piece was put in also has a lot of windows, and is out of direct sunlight. BUT...the piece in the basement has darkened MUCH more than the piece installed upstairs!

So... What's up with cherry and the way it darkens? Anyone? I don't have a clue but do see that apparently it darkens best when not exposed to light. At least that appears to be what I am seeing...

My feeling now is that cherry best darkens when exposed to the air and located away from light as much as possible.

What is your experience?

Hope this is the right forum to post this question!

Bill

[sheldon pettit]

Hi Bill, well.... there is lots of chemistry going on with cherry, PA or not. What your seeing may be the affects of several things. darkening under steel could be caused by the iron content in the steel to react with the tannic acid in the wood to darken that portion for one. As to the basement, is it more humid there than upstairs or do you run a humidifier down there? And is or was the piece in the basement finished in like manner as the transition piece? Did both sides look as dark or just the exposed side? To many things to consider to make a judgement call as of now.

[Curt Harms]

I have a few cherry boards in a basement shop with one small obstructed window. They've darkened quite a bit and get no sun. The space DOES have fluorescent lights though. They're not grow bulbs but I wonder if they put out enough UV to have an effect.

[Bill Space]

Boy don't you hate it when you type a response and it is lost in an instant? Something about an expired token...and pushing the back button did not restore what I had lost.

So to try again, probably more briefly.

Thanks Sheldon for the reply!

The metal I used to shield a portion of the surface of that test piece of cherry was bright stainless and I did not see any tarnishing of the surface so I am not sure that there was any interaction between the wood and the metal. Possible I suppose.

The basement does not exhibit a noticeable moisture as it is above ground on two sides and the sides in contact with earth are waterproofed extremely well.

Having never worked with cherry, I guess I just assumed that it magically darkened over time due to exposure to light and air. Never had reason to want to understand the why of the process.

Now I am curious. What actually is the cause of the darkening? Is it reaction with air? Does exposure to light inhibit the darkening process rather than enhance it? Does applying a wood finish hasten or slow down the darkening process. And so on...

I will try to find some answers by doing an internet search and will post anything of interest I find here.

Anything anyone can add to this thread that will help me understand the color transition that cherry wood goes through will be highly appreciated!

Thanks!

Bill

[sheldon pettit]

Bill, i think that would be they way to go, i don't know how much you will find but i'm sure there is something. For me to get into it is to time consuming, but for some basic info, it has to do with the wood itself and chemical makeup and natural chromophores as well as both UV activity and oxidizing principles, ok? Unlike others, the way I've always handled the darkening principle of woods was to apply chemical stains mostly hydroxides but also ammonia and ethanolamine, or in needing a light color then peroxides or hydroperoxides. these can be either hydrogen/sulfate/or sodium types. when the wood is treated so, then the color shift obtained by such will remain the same over time.

[Bill Space]

Sheldon & Curt,

After doing a little reading on the subject, my understanding now is that three things cause cherry wood to darken: Exposure to UV light, Exposure to Air, and possibly humidity.

UV seems to cause a change in the wood that promotes darkening.

Exposure to air offers oxygenation opportunity.

I am not sure what affect humidity has.

It seems to be a proven fact that exposure to UV from sunlight will darken cherry. Of course that cherry wood was likely exposed to air at the same time it was sitting in the sun. And the moisture in the air at that time was what it was, certainly more than zero.

So back to the "test piece" that I had sitting on the window sill for a couple months probably. Why would the part that was shielded by the stainless steel cover turn out to be darker that what was exposed?

I know that the carpet in our house (passive solar design, facing due south with lots of windows) has lightened a lot over the years. What was a medium brown is now a light tan color. So I am wondering if cherry wood that is exposed to excessive UV after darkening would bleach out and lighten up in color. It is possible that what was under the piece of SS sheet metal was actually the color of the wood BEFORE I exposed it to the sun for a couple months. MAYBE the sun bleached the exposed surface of the wood, which made it appear as if the covered area darkened, when in fact the uncovered area ended up lighter!

What's the chances of this?

I am going to have to see if I can find that piece of cherry laying around here somewhere. If I can I will rip it in half and try putting it in the sun again, after face jointing one half, and keep better track of what is happening. Not as much sun here in winter as there was last summer though...

Thanks for your thoughts!

Bill

[Lee Schierer]

Just to add to the confusion I have some cherry that was harvested over 60 years ago. It is dark all the way through the board. Sanding or planing results in no color difference. The Cherry I have from local sources (NW PA) will darken in about 2 years even through a clear finish. Sunlight exposure can increase this rate of darkening. I've seen light colored shadows on pieces that have had something covering the surface, such as a vase placed on a table top and left in place for months at a time. These shadows don't seem to disappear over time. I think the wood also oxidizes to some extent as exposure to air seems to cause some level of darkening.

[Bill Space]

Bingo!

Well, maybe not but I found this statement in another thread...but was not smart enough to get the name of the poster. I will try after posting this and edit this post if I can....

I also agree with the comment that cherry will reach a saturation point where any additional color change is imperceptible. And many people don't seem to realize that all woods, cherry included, will bleach out if exposed to direct sunlight for too long. I've seen some bleach so badly after 15 years or so it's hard to tell the wood is even cherry.

John TenEyck (http://www.sawmillcreek.org/member.php?72349-John-TenEyck)


So perhaps what I suspected, that I left the wood exposed to UV too long, and caused it bleach out is the answer to why the exposed surface was lighter than the covered surface!

[Bill Space]

Hi again,

I said in a post above:

Then this afternoon, I noticed a cut off piece of cherry, that remained from a transition piece that I made to cover the transition between a carpeted floor and a tiled floor. This piece was in the basement shop, which does have a lot of windows, being an above ground basement on two sides, but the piece in question was back away from the windows. The location on the first floor of the house where the transition piece was put in also has a lot of windows, and is out of direct sunlight. BUT...the piece in the basement has darkened MUCH more than the piece installed upstairs!

Well, I guess I had not looked at that piece upstairs for a while! I brought the cut off up and compared it to the piece I was referring to, and the color was about the same ... I should have taken a second look rather than use the image stored in my memory!

Funny to me because after installing that piece I had been watching it and not noticing much if any change. I think it is finished with a simple wipe on finish of 50% mineral spirits and 50% polyurethane.

Bill