It’s a new home, just over 2.5 years old.
Interior douglas fir plywood doors and cabinets started discoloring a little more than a year after construction.
Discoloration is progressive and ongoing.
Home is in a damp location with frequent rain, but out in open pasture land (not a forest area).
Doors were finished with Watco clear lacquer, satin #63231 (7 coats)
Cabinets were finished with SW Fast Dry Vinyl Sealer T67F6 (1 coat) and Acrylic Conversion Coating T77F63 (2 coats) Although finished with different products by different contractors in different locations, both are discoloring.
Moisture and microbial growth in the wood fibers? Contractor tried sanding off the clear finishes, but the discoloration remained in the wood. The wood behind the hardware plates is NOT discolored, although it is exposed to the same relative humidity, suggesting that light is somehow involved? Fungal growth doesn't usually like light. Is there another microbe that colonizes and discolors wood that also needs light?
Has anyone seen this before? Can anyone recommend a good clear sealer against moisture, followed by a clear satin finish that also provides superior UV absorbers and inhibitors?
All are interior doors and cabinets.
Mystified in Honolulu....
Click the link below to download the file included with this post.
I think you have three options. First is that it is a reaction of the wood to light. The switch plate discussion supports this. However, light only goes 1/100" into the wood, so sanding should have quickly exposed uncolored wood. So, this does not sound possible.
Second is that we have enough moisture to cause some fungi (mold, mildew or other) to become active. They might indeed go deeper into the wood, but almost all of them will affect sapwood (which is light colored) and not the heartwood. Plus you would notice the high humidity in the bathroom, etc. and see mold growth in other spots. So, this also seems unlikely.
The third option is that the moisture, as it moves through the wood, is carrying some chemicals in the wood with it toward the surface. If this is true, then if you look carefully, you will see that where the framing is located, and moisture is slowed, there would be less color change.
Being a wood expert, I cannot comment about the interaction of a finish with wood or with itself.
I hope you can post or email some pictures.
2/4/16 #3: Mystery Discoloration of Doug Fir V ...
It appears to be only on the veneer areas. Is that the case? I did not see it on the casing around the doors but maybe missed it. It's rare these days, but just in case it is indeed just on veneer, did the cabinets and interior door veneer come from the same shop/laid up by the same shop?
I also find how it coming from around the edges in interesting.
2/4/16 #5: Mystery Discoloration of Doug Fir V ...
Thanks for looking at the photos, and providing input. Yes, it appears to be affecting only the veneer, and primarily spreading from edges and cuts. This supports the moisture theory as they are not sealed as effectively. But I'm baffled by the lack of discoloration where the hardware shields the substrate and finish from light, and if light is the cause why it doesn't equally discolor the more exposed field areas.
Would liquid water be need to cause extractive bleeding? These doors and cabinets don't get wet, they are just exposed to high relative humidity. Does anyone know of hygroscopic components in plywood or veneer adhesives that might collect moisture from the air?
And yes, as mentioned in the OP, finishes for doors and cabinets are different, and applied by different contractors, in different shops, in different areas of the island before being delivered to the jobsite.
2/4/16 #6: Mystery Discoloration of Doug Fir V ...
I understand they were finished by different shops but it wasn't clear if they were MADE by different shops. I'm guessing it is an outside chance but it's a variable I think needs to be checked off especially since the hardwood is not reacting. Which to me would be sealed worse, as in the back of casing is usually not finished at all. Therefore you'd see it happening more on the hardwood.
To me this is some kind of reaction with the glue holding the veneer to the substrate from humidity. I'd be more positive if they were laid up by the same people- but rare in this day and age.
2/5/16 #7: Mystery Discoloration of Doug Fir V ...
Phil, in my opinion, from what those photos are showing, this truly looks like it's a reaction "creeping" in. I say this as only the outside ( from edge creeping to center) seems affected.
I would bet and agree with "FAMILY MAN" this may be a reaction from the veneer itself, or the veneer glue ups ??
Most likely it's not a "single reason" reaction itself, but more from it as no photos is showing "blotch" in the center of any veneered pieces.
Maybe a double reaction ( or more a chain reaction), meaning, either the finishing or the weather ( humidity) is slowly bleeding through / making this reaction from the edges
Another possibility, is due to some glue bleeding through, then the veneering shop tried to sand it down or at least initially trying to correct the known issue ( from the veneer shop or finishing shop).
All in all, in my view, trying to find the culprit could take more time then....redo all of it, meaning, personally (professionally)....I would stay away trying to fix those and opt for the better / best end result !!....Going for changing them all for new one that you could not only monitor the quality of the veneering, but also the finishing steps !
All the best
2/5/16 #8: Mystery Discoloration of Doug Fir V ...
I have seen this once before. It was a library wall that was covered with finished plywood. I do not recall the species, but it was on the West Coast...I recall vaguely that it was cherry veneer.
Obviously, this is a rare event. So what is different here that we do not see in other exposures? Is there a different climate? A different species? A different adhesive? A different finish? If everything is normal or standard, then why don't we see this more often?
My guess is that temperature has some effect and maybe light.
Can you take a wet rag and wet the door several times a day using an identifiable pattern and see what happens? Also check for an odor.
We know that wood and its components do not move or migrate when dry, and there are no vapors emitted from dry wood for a wood like DF. But I have seen solid wood and plywood that is infected with bacteria in the living tree react with the finish over time and darken. The bacterial slime does apparently migrate. With the bacteria present, we also would notice an unusual odor when the wood is exposed to high humidity. So, check the smell when high humidity is present.
We know that partly cured adhesive can continue to migrate. I suspect that partly cured finishes could also move.
2/5/16 #9: Mystery Discoloration of Doug Fir V ...
I haven’t seen this condition before but will take a stab at the probable cause(s). To lay the ground work for my theory, here are a few contributing factors to consider.
Wood readily absorbs moisture and as the relative humidity (RH) goes up and down, the moisture content (MC) of the wood/lumber does the same – it wants to be in equilibrium. Finishes/coatings allow water vapor to pass through them and some are more permeable than others. The ability of a coating to resist moisture from moving in and out of the wood is called moisture excluding effectiveness (MEE). 2-part epoxy does the best job of restricting the water vapor movement while drying oils like linseed and Tung perform the worst. Lacquer is somewhere in the middle and conversion varnish is better. Adding vinyl sealer improves its performance. It takes a few coats of finish to get the best results….
In the kitchen and bath, the corners of doors and drawers are usually the first place to show water damage. The finish is thinnest at the corners and is the easiest entry point. Once water gets into a crack, the deterioration of the wood and finish is a downward spiral.
Many woods, including Douglas fir, contain water soluble extractives. As moisture gets into the wood, the extractives migrate to the surface. On painted surfaces, we often see “tannin” bleed come to the surface of the paint and cause discoloration whenever we don’t use a stain blocking primer. Extractives can turn brown and even black from oxidation when exposed to sunlight.
With the humidity so high, I believe the water vapor is entering the wood at the most vulnerable points – the corners of the doors and drawers. The excess moisture in the wood combined with exposure to sunlight is causing the extractives in the wood to migrate to the surface. The sunlight is oxidizing the extractives, causing the brown staining.
To fix the problem, I’d recommend replacing the affected items and using a different wood. The alternative would be to seal the wood with epoxy and topcoat 2-part acrylic polyurethane.
2/6/16 #10: Mystery Discoloration of Doug Fir V ...
Has anyone any proof that moisture in the form of vapor can move extractives in wood? I have never heard this and have been told before that humidity alone will not move extractives...liquid water is required.
If indeed this problem is due to high humidity, I would expect to see and hear of other issues, such as a warped door, or the cracks between the drawer fronts getting small. The gap between the doors looks substantial indeed, so I am tempted to discount humidity. Further, with high humidity at a closet, the bathroom would be a mold factory. Further, this is not the first DF door on the Island, so why haven't we heard of this before?
Why is there the coloration on all four edges? What do all four edges have that the faces do not have? If moisture is moving in the edges, wouldn't also eventually move in the faces?
Why is there a small circle darkening near the hardware on the door? Is there something under this spot that is different than the adjacent areas?
Why is this darkening not seen where the hardware is located? Even if the hardware restricts moisture movement, we should not see such a sharp demarcation? The only difference appears to be that there is no finishing under the hardware...were the doors finished in place and then the hardware was installed?
Note that the area around the hardware on the door is darkened. The hardware did not seem to slow the reaction. If the reaction were moisture related, the hardware would seem to be likely to slow the moisture movement.
Id this is a reaction between he adhesive and the finish, if we examined the glue line at the edge and then near the center, we will see a difference in thickness, especially with a thinner glue line in the center. Less adhesive should mean less chance for a reaction.
2/7/16 #11: Mystery Discoloration of Doug Fir V ...
Here is another thought. If we were given the job of darkening DF, how would we do it? It does indeed sound like the discoloration is within the wood and not just at the surface where the finish is. So, I am thinking that the discoloration is a reaction with the wood components.
One way to darken wood is with an oxidizer, like ammonia. I am not enough of a chemist to know what other oxidizers might exist or be created. But we do know that most wood species and the extractives in the wood do not emit a gas- -that is, do not vaporize.
So, can the components of a finish react with the adhesive used to laminate or used within the core material to form an oxidizer? Is there a catalyst that is released as the finish or adhesive cures (which is what happens with formaldehyde in the adhesive) and then this catalyst acts as an oxidizer (or reacts with the finish) on the wood. If so, why does this start on the edge and move inward? What is different about the edges compared to the center. I am not aware that any finish can effectively block oxygen or other molecular components of the wood or would create a heating difference of any size at all. Likewise, moisture or heat would eventually get into the total wood piece through the faces and not just an edge.
I cannot imagine that there is moisture difference or heating difference that is large enough to create this situation in-use. So, I am thinking that we have a manufacturing issue that is causing some chemicals to move or change.
So, I wonder if this is related to the amount of adhesive. That is, during pressing do we get different glue line thicknesses? Or perhaps during pressing (laminating), do we have more heat near the edges? During pressing, are some of the components in the adhesive moving to the edge? We do know that excess moisture will move to the edges, as vapor, during hot pressing, so maybe one of the acids in wood is also moving as a vapor.
Now, the finish is likely quite uniform on the piece. I would expect it to cure uniformly, rather than see the center curing at one rate and the edges at another. So, I am tempted to discount the finish itself. However, we do know that the adhesive does often have a catalyst, does move especially in response to heat, and is often releasing a carrier. We also know that oxidation reactions take time. We do know that light encourages some oxidation reactions. But my knowledge of organic chemistry is quite limited, so I cannot go further.
2/7/16 #14: Mystery Discoloration of Doug Fir V ...
”Has anyone any proof that moisture in the form of vapor can move extractives in wood? I have never heard this and have been told before that humidity alone will not move extractives...liquid water is required.”
Water liquid is the primary cause of extractive migration, but water vapor can also be a source. Check out the first paragraph in the section on water-soluble extractive bleed in this document - Understanding Extractive Bleed
”If indeed this problem is due to high humidity, I would expect to see and hear of other issues, such as a warped door, or the cracks between the drawer fronts getting small. The gap between the doors looks substantial indeed, so I am tempted to discount humidity. Further, with high humidity at a closet, the bathroom would be a mold factory. Further, this is not the first DF door on the Island, so why haven't we heard of this before?”
In the theory I proposed, I ruled out warpage because doors and drawer faces usually have a stable substrate so they stay flat. I suspect mold/mildew is a concern in Hawaii in the same way it is in Florida and residents have to take the same _Florida_Home.pdf target = “_blank”>preventive measures.
”Why is there the coloration on all four edges? What do all four edges have that the faces do not have? If moisture is moving in the edges, wouldn't also eventually move in the faces? ”
The discoloration on all 4 edges is really odd. The only explanation I could think of is that moisture is entering the wood more readily at the corners where the finish is thinnest. It literally looks like each edge of the doors and drawer faces were set in a pan of water and allowed to soak it up for a time. Over time, I’d expect to see the entire face of the doors & drawers turn the darker color.
”Why is there a small circle darkening near the hardware on the door? Is there something under this spot that is different than the adjacent areas? ”
Is this the spot you’re looking at?
It looks like moisture has traveled through the wood to that spot – there seem to be streaks of color between the larger dark area above and the round spot below. I wonder if the moisture is traveling between the wood and adhesive…(if it’s moisture at all)?
”Why is this darkening not seen where the hardware is located? Even if the hardware restricts moisture movement, we should not see such a sharp demarcation? The only difference appears to be that there is no finishing under the hardware...were the doors finished in place and then the hardware was installed?
Note that the area around the hardware on the door is darkened. The hardware did not seem to slow the reaction. If the reaction were moisture related, the hardware would seem to be likely to slow the moisture movement. ”
The wood covered by the hardware has not changed color and is still very light. This is a normal condition… the lignin in wood is photoxidative and changes color with exposure to sunlight (UV). I’m theorizing that the extractives migrating to the surface of the wood are causing the darker color compared to the color of the wood in the center of the door/drawer.
”If this is a reaction between the adhesive and the finish, if we examined the glue line at the edge and then near the center, we will see a difference in thickness, especially with a thinner glue line in the center. Less adhesive should mean less chance for a reaction. ”
I considered that the discoloration might be caused by some component (e.g., plasticizer) of the adhesive migrating to the surface of the wood or possibly off-gassing from the core (it looks like the door has a foam core). But I thought it was less likely that the color change was caused by the adhesive or core because the doors and drawer fronts are so different are were provided by different fabricators.
Moving forward, I would investigate these potential sources;
Find out what adhesives were used on the doors and drawers to see if the chemistry is similar.
After several days of high humidity, measure the MC of the dark and light colored areas on the doors and drawers.
Monitor the dark areas to see if they are indeed expanding and determine the rate.
It’s an intriguing problem and it would be great to define the root cause. Phil has an interesting job!
2/7/16 #15: Mystery Discoloration of Doug Fir V ...
Gene: I was taken with your theory that the glue thickness may relate to the pressing process, until I considered the discoloration blooms around penetrations which were cut in the contractors shop, well after the glue had cured. And, the discoloration is progressive, spreading beyond pencil and chalk lines that used to mark its boundaries... Still, chemical reaction between components could really be the cause.
Robert: I agree, and replacement doors are on the way. The million dollar question, is how to finish them.
Paul: I am convinced that moisture penetrating finishes at porous edges is involved. Your suggestion of epoxy to block moisture, followed by 2 part acrylic polyurethane may be the best solution if I could be sure the topcoats contain UV absorbers and inhibitors to protect the wood as well as the coating. I'm running into difficulty getting manufacturers to tell me what the add to their secret sauces..."it's propriatery"... Do you or anyone reading this know any specific clear finish products which contain a combination of hindered amine light stabilizers and other uv inhibitors, which are suitable for interior use on doors and cabinets?
Not included in the photos I posted; one door has a dark spot right in the middle of the door, similar to the spot you noted by the door hardware, but surrounded by natural colored wood. My theory is a pinhole in the finish caused by a surface blemish...
My theories are biased by my belief that both moisture and light are involved, although I'm not sure exactly how. I had guessed it was microbial growth, but Oregon State University looked at a sample and did not detect fungal growth. Oxidized extractive bleeding sounds believable, if we assume humidity without liquid water can move extractives (I will read the link posted with interest). I really appreciate all of the well considered responses, theories, ideas and suggestions that have expanded my thinking.
Specific product suggestions for finishing would be welcome. Clear, satin, interior use, high humidity, blocking moisture and uv (and light wavelengths that oxidize extractives?) OK... Tall order.
2/7/16 #17: Mystery Discoloration of Doug Fir V ...
For the 2-part acrylic polyurethane I'll recommend Matthews satin clear (see the link to the tech data sheet below). It's formulated for exterior use and works very well. I've used it in MANY museums with excellent results.
I'll also recommend you use the accelerator (link below) to speed the cure time.
There are other excellent 2K-PUs on the market that are also a great choice for woodwork but I'm not sure if any of them contain HALS and UVAs.
Click the link below to download the file included with this post.
Paul, Thanks for your comments. You got me thinking even more and I think I might have a clue. What do you think?
First, Water vapor at room temperature cannot dissolve or move water-soluble extractives. I do recall some chemistry about making solutions with water and non-hygroscopic chemicals.
Now here is my latest thought: Although liquid water is required to make a solution, with highly hygroscopic chemicals, we can have a liquid formed at under 100% RH. (Keep this thought in mind as you read further.)
Technically, water vapor is moving by diffusion, driven by a vapor pressure gradient. There is no way that a water vapor molecule can attach to any extractive molecule...there is no hydrogen bonding or molecular bonding possibility for them to attach. What is needed is a liquid that moves. This is reinforced by the Field discussion on p.5 and the Summary on p.7 in the referenced article. Further, even if vapor could move extractives, this would mean that extractives from one spot in the wood are traveling to another spot. Yet, the OP indicated that the wood veneer was discolored deeply.
It is my experience that when extractives move they are concentrated in a region at the surface, left behind when the liquid evaporates. That is, a liquid can carry an extractive to the surface of wood and then be evaporated, leaving the extractive behind, creating a concentration at the evaporation site--the surface. The extractive than can oxidize forming a new color.
Note that if indeed vapor could move extractives, we would see this occurring time and time again, as vapor is always changing in wood products.
Moisture vapor only moves through wood when there is a difference in vapor pressure. So, what force is creating a substantial difference in vapor pressure between the discolored and normal colored wood? Certainly, liquid water entering on the edge will often make a difference, but this is not likely in this case. So, how do we get a vapor pressure difference that will last for a long enough time? Overall, the humidity at the edge and at the face would seem to be, on the average, identical.
So, let me throw in this possibility. We know that highly hygroscopic chemicals will form a liquid at less than 100% RH. (Example: Table salt will attract enough vapor to become liquid and then cake or harden.) So, is there a highly hygroscopic component in the adhesive or core material? Or maybe it is associated with the edge banding? It would attract liquid moisture at less than 100% RH. With a liquid, I can envision some small movement of chemicals and, more importantly, some changes in chemicals (chemical reactions).
As an example, the formation of iron tannate stain in wood occurs when there is tannic acid, iron AND LIQUID WATER. Humidity alone does not cause or create this reaction. In other words, an iron nail in oak does not form iron tannate until liquid water is present. But we do know that a highly hygroscopic chemical (mainly a salt) can form liquid water which can be used to make this reaction occur even when the humidity is under 100% RH. I do believe that some cedars have such chemicals and so are able to create enough moisture so that fungi (mold) can grow on the wood surface even at humidities under 100% RH.
I am not convinced that light is a factor, as we know that light only penetrates into wood about 1/100". How do we get the color deep into the wood?
I think that with the presence of water liquid, chemicals are formed that are being oxidized, which would happen at the surface and below the surface.
I am still not sure why we do not see this more often. Is it possible that the doors are being cleaned with a chemical cleaner by the maintenance staff? How can entry doors and dresser drawers have the same effect? What is in common? Maybe the adhesive or the core of ??? Why only in this case and not all over the island?
One suggestion. Put some oxalic acid (also called wood bleach) on the stain area (perhaps first sanding through the finish). If indeed this is an oxidation reaction, you will see an almost immediate lightening of the color.
2/8/16 #19: Mystery Discoloration of Doug Fir V ...
Gene - thanks for all your insight.... This is a very unique and interesting problem and your multi-pronged approach to identifying the cause is very informative!
I think the series of questions you ended with sums up this discussion nicely;
"I am still not sure why we do not see this more often. Is it possible that the doors are being cleaned with a chemical cleaner by the maintenance staff? How can entry doors and dresser drawers have the same effect? What is in common? Maybe the adhesive or the core of ??? Why only in this case and not all over the island?"
At this point, I think we need the lab results that define what is causing the discoloration to better understand how it's happening.
2/8/16 #20: Mystery Discoloration of Doug Fir V ...
I am just wondering out loud about the moisture. I can understand the end grain of the veneer getting the wicking of water since it is like a straw but I'm a little confused with it coming in against the grain. I would think the discoloration wouldn't be as uniform all around the door. But more at the top and bottom as compared to the sides. Just a thought.
Since the doors are to be replaced, can you somehow damage the finish in areas that have not discolored, mark them and then see over some time if it starts to discolor? Again, just a thought.
2/8/16 #22: Mystery Discoloration of Doug Fir V ...
Well ... I learned more today about things NOT in common with the doors vs cabinets:
1) the plywood and veneer were glued up by different shops/suppliers. 2) the glue for the cabinet plywood and veneer was is a soy based product, while the glue for the door components and veneer was a polyvinyl acetate emulsion adhesive.
Paul: Thanks for your input on the Matthews product. I'm looking into it.
Jeff A: That is a really good idea to ding the finish in a good area and see if it gets dark over time. Unfortunately, the darkening took over a year to manifest, so we won't be able to wait and see what happens before we finish the new doors.
I've attached another photo to show the unusual spot growing in the center of a one of the doors ... where I'm suspecting a blemish caused a pinhole in the finish. It was contained within the chalk mark before.
What do the doors and cabinets have in common? ... prolonged exposure to elevated relative humidity for sure. VG Fir veneer for sure. I've been unable to find anything else so far.
I've been racking my brain trying to figure out where i have seen this before on VG Fir.
We use a lot of it here in the Pacific Northwest. I'm going to through out one more scenario and I'm going to ask you to look at the photos one more time. It looks like random orbit marks.
I am going to put forth the theory that the areas that are darkening the veneer is thinner because it was sanded thinner by a random orbit sander. I have no doubt both moisture and sunlight are doing the work but what you are seeing is the wood/veneer where it is thinned down to oversanding being affected.
Anyone who has ever sanded an edgebanded cabinet door and analyzed how almost everyone does it, well you spend more time on the outside edge as you sand the glue from the banding off.
I have seen this on much smaller scale on one or two pieces on several different jobs over the years.
I would say the trick is to make sure the veneer is thick enough and sanded properly and then do a proper finish.
2/9/16 #24: Mystery Discoloration of Doug Fir V ...
Since there is zero change under the pull, light is required for whatever reaction is taking place.
It's hard to tell from the pictures, but it looks like the light areas still have the red and white/yellow tones of fresh fir, instead of the more even tan/brown tones I would expect. Are the dark areas significantly darker than fir that has been exposed to light for 2.5 years should be (and/or the light ones lighter)?
What has been done to/used on the doors since they arrived at the home - cleaning, polish, etc.?
2/10/16 #25: Mystery Discoloration of Doug Fir V ...
Gene - the oxalic acid suggestion made a marked difference! See the image from Director of the Oregon Wood Innovation Center at Oregon State University, who is kindly examining samples for us and exposing them to hot humid and hot dry conditions... He will do moisture readings after a week of 90% humidity exposure, and I will report back.
Dave L: The home owner reports no cleaning chemicals or solutions have been used on the doors since installation. Occasional damp wipe only.
Second photo was furnished by the contractor ... it shows a remarkable difference in color depending on light exposure. He pointed out the "light shadow" on the discolored wood, behind the door lever. Wow. It's clear light plays an important role, even at the interior of the house which only gets indirect light.
Anyone who lives at elevation above 2,000 ft in Hawaii sometimes finds themselves in the clouds. Although the doors don't get wet, the article Paul provided did suggest that liquid water may not be needed. There must be enough moisture entering the wood to cause extractive bleeding in areas around edges and cuts? If the oxalic acid test indicates migration of extractives, and if light has oxidized them, we need a super impermeable sealer, perhaps followed by a super impermeable UV absorber and inhibitor.... (if UV is the oxidizer?).
The darkening effect on areas which have never been exposed to direct sunlight raises another question: Does anyone know what light wavelengths will oxidize extractives?
Unfortunately, the oxalic acid test does not confirm or rule out extractive migration. Oxalic acid (aka, deck brightener) does remove water soluble extractives (WSE) (as indicated in the article) but it also removes lignin that is oxidized and discolored. We still don't know why the edges are darker than the center of the doors....
Is it possible for the lab to scrape some of the darker color at the edges and some of the medium color in the center and compare the chemical composition (e.g., mass spec)? That would indicate if there is a chemical difference in the wood surface where it's darker and define which WSE (if any) is involved.
Regarding which wavelengths of light cause photo-oxidation, the spectrum involved includes UV-A, B, and C as well as visible light up to 500 nm. UV has the strongest effect and also breaks down coatings used outdoors. Using a finish that contains UV absorbers and stabilizers will offer the most protection - even indoors.
I assume that you did not soak the wood in oxalic acid, but put on a light coating that evaporated quickly. If so, I do not think that the oxalic acid would have time or enough moisture to move the3 extractives. So, it does indeed look like an oxidation reaction, as discussed earlier.
One other thought, if the extractives are moving, then there must be some part of the wood that is deficient in extractives, which means that part of the wood should be non-darkened. As i understand the OP, the wood is dark way beyond the surface. But even more, we cannot move the large extractive molecules with vapor at room temperature.
2/17/16 #28: Mystery Discoloration of Doug Fir V ...
Everyone's thoughts and input have been invaluable and very educational, particularly from Gene and Paul. Thank you for your interest and comments.
A technical representative from the coating manufacturer inspected the wood under magnification onsite, and observing tiny black dots, concluded the issue was extractive bleeding, which I had trouble believing before I posted on WoodWeb. Later, the lab at OSU inspected a sample under a microscope and saw "discolored ‘black dots’ within the parenchyma cells" which they thought suggested oxidation. I don't know enough about wood science to understand what that means, or whether it supports the extractive bleeding theory.
Before posting, I dismissed the extractive theory due to lack of liquid water, but the article shared by Paul made me rethink that. It seemed obvious that light was involved from the sharp difference in appearance behind hardware, and the "light shadow" of the door lever handle. Paul's wavelength chart has given me some confidence that a good UV blocker should go a long way toward reducing oxidation.
Gene: You are correct that the wood was not soaked in oxalic acid, but that the acid was applied to the sanded area and allowed to dry which resulted in pretty dramatic lightening, although it also looked from photos like the sanding itself lightened the wood somewhat. Acid was similarly applied to an unsanded area on the same sample, with no apparent lightening. My comment that the discoloration extends deep into the veneer was not my own observation, but based on the contractor's statement that he tried to sand off the discoloration and was afraid he would sand through the veneer before he removed the discoloration. So, it sounds like darkening extends more than 1/100", but I don't know how deep. I agree with your observation that vapor movement can only happen if there is a difference in vapor pressure, but I can't think of any mechanism that would cause a difference in vapor pressure between the edge of the door and the surface a few inches away. Only presence of hygroscopic material behind the coating made sense to me. Now I'm thinking formation of condensation on the door is plausible, if air is saturated and the door is a degree or two below dew point? This might allow moisture to wick into the edges, then evaporate out through both edges and surfaces?
It is really odd that although wood is from different sources, glues are different, coatings are different, and applied by different people in different locations by different methods, conditions could be so unique that others have not seen this frequently. I'd think that lots of places in the Pacific Northwest would be damper for longer periods.
Because the discoloration happens near cuts and edges, and the home is in a moist climate, I'm theorizing that there must be enough moisture to cause extractives to migrate, and that the clear finish is somewhat permeable to water vapor but not permeable to extractives, which are trapped behind the surface of the coating and oxidizing with exposure to daylight.
So, unless the wood lab is able to perform the spectroscopy Paul mentioned and ID the difference between dark and light areas, we may not completely solve this mystery. I'm reasonably confident that sealing against moisture and protecting the substrate from UV light is our best bet at a solution. If we are able to get more information, I will be back to share.
And Mahalo for all of the suggestions and ideas.
2/18/16 #29: Mystery Discoloration of Doug Fir V ...
The idea of migration of extractives has several problems...
First, water vapor cannot move the large extractive molecules at room temperature. If water vapor could do that, why is this problem not seen more often? The extractive molecules are very large in size.
Second, if extractives do move, that would mean that some part of the wood now lacks extractives so would be very light in color...lighter than normal.
Third, If extractives could move easily, then why doesn't normal drying, where we have liquid water movement, leave the surface darken than normal almost all the time?
Fourth, if this is a light reaction, why is it deep, as we know light cannot penetrate into wood more than 1/100"? If light, we could sand off the discoloration.
Fifth, the oxalic acid reaction does confirm that this is an oxidation reaction, but not what is involved. Extractives usually do not respond to oxalic acid.
Sixth, this is a really rare event, so what is really odd or different here? Moisture (high humidity) exposure is not rare for D-f.
Seventh, The pattern on the door and drawer strongly indicates that the discoloration is due to something occurring after manufacturing.
Eight, the lack of discoloration behind the fixture could be related to something put on the surface of the door after installation. This chemical could react with other chemicals on other products as well, like drawers.
With drawers, the moisture would be moving from the humid outside to the drier inside, so the front would be free of discoloration if it were extractive migration.
With the drawers, is the discoloration also on the inside where it would be unlikely that the surface chemical would be located...if a cleaner, for example, people would only clean the outside, not the inside?
2/18/16 #30: Mystery Discoloration of Doug Fir V ...
Gene: You make a very strong case against the issue being caused by extractives!
Although baffling, everything you have said makes sense to me except point eight. The owner, who had the home built and has been the caretaker of the home since said she has never used any cleaner or chemical on the doors and cabinets, but may have occasionally wiped them with a damp cloth.
I'm going to see if I can get any input from Forest Products Laboratory ... I don't know where else to ask. The problem is intriguing. If I learn anything new I will return and let you all know. Thank you so much for your thoughts and ideas.
2/18/16 #31: Mystery Discoloration of Doug Fir V ...
Any chance we could put a wet rag on a spot at the edge of this coloration, on both discolored and non-discolored wood for 6 hours? A little soap or detergent might help as that is a surfactant. Then let it dry with exposure to light.
This will carry moisture into the door away from the surface. Then, as it dries, back to the surface, assuming that the finish is not water and water vapor impervious.
2/29/16 #32: Mystery Discoloration of Doug Fir V ...
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