Pink Maple Mystery
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Sunlight can give some woods a pinkish cast. March 17, 2005
Question
We are having a problem with clear white maple veneer turning pink after sitting in our warehouse for three or four weeks or after being installed. It has been sprayed with a catalyzed vinyl sealer, sanded with 220 grit, then sprayed with a vinyl topcoat of about 3 wet mils. Clear finish, no stains. The pink is predominately on flat surfaces or on doors or drawer fronts. It appears on only some units that were sprayed by the same person on the same day, but not on all the units and only in certain areas, not on the whole unit. Has anyone else had this problem? How do you fix it or make it go away?
Forum Responses
(Finishing Forum)
From contributor R:
Often over-catalyzation will cause light woods to take on a pink hue. Sometimes you might also notice the surface gets foggy as the finish sweats out the catalyst, though this is a rarer occurrence. The only cure I know is the dreaded S word.
From the original questioner:
Thanks for your response. But if it is over-catalyzation, why isn't it happening on all the pieces sprayed from that batch and why only in some spots but not all over the unit?
From contributor J:
Some maples will turn pink when exposed to UV rays or oxidized. If this is just a case of the tannins reacting, as mentioned above, everything will even out in short order when all are exposed to sun or UV. Do you know if these certain pieces were the ones either on top of a stack or blocking the rest off from sunlight? I've had this pink cast happen to me many times and there's nothing you can really do except tone out lightly with a dilute mixture of green to negate the pink color.
From the original questioner:
I think that this is the problem because the parts of the cabinets that were not exposed to light have not turned pink. Also, there are areas within a side where only the part that was exposed has turned and the rest of the panel has not. We have had a problem in the past of over-catalyzation and it did blush out and eventually cracked. Since that time we have been extremely careful in how we measure, so I doubt that this is the problem. Thanks for your response and hopefully you are right that it will all mellow out in time.
From contributor J:
It will. Just pull out and expose the light pieces to have them catch up to the rest and don't bother reverse papering them if you get the urge.
From the original questioner:
I have done that with cherry (reverse paper also!). Don't want to have to do it again! I agree with you – I think that the UV or lighting in our plant is causing the problem similar to what happens with cherry.
From contributor C:
I have seen similar color changes in oak and maple plywood and thought it was the glue in the plywood. Possible?
From contributor J:
Glue in the plywood will sometimes have a slight uneven sheen to the surface. You can make a quick check to see if it's glue by wiping on lacquer thinner. If the wood doesn't get darker in these areas, it probably is glue. Oak will usually have it seep up through the grain, and maple. Usually you'll only have this problem if it is a figured or an expensive cut of veneer because they tend to slice them thinner to get more yield. Lots of problems with seams oozing up glue and veneers sliced so thin you can almost see the dark substrate through them.
From the original questioner:
In the last couple of days we have done some testing. We put a piece of unfinished maple veneer on 3/4" flake substrate, taped off half of it and exposed the other half to UV lighting. Within a short period of time the maple veneer turned yellow in the area that was not covered. We also took a piece of finished maple and did the same thing. It turned pink. I also heard that there are two different cuts of maple, one cut in the summer months and another cut in the winter months and that depending on when it was cut, the veneer will respond differently to UV light depending on how much sap, sugar, and tannins are in the veneer. Now that we know what created this problem, how do you correct it and how do you keep it from happening again? We can strip and sand out the pink and refinish the pieces, but will it come back? Can we use a UV inhibitor in the finish and how good do they work? I heard that they will slow it down but eventually it will turn.
