Pre-Cat Lacquer Yellowing in the Dark
Some alkyds yellow in the presence of light and some yellow in the absence of light. May 18, 2010
Question
I am having an issue with Chemcraft Opticlear 8320 (satin) yellowing in the dark. I have sprayed a white primer (C.C.Optiprime) and then two coats of Opticlear tinted to an off-white. We applied a scuff-coat of clear Optiprime satin on top of the white. The back sides of the cabinet doors are yellowing significantly as well as pocket (man) doors that have been in their pocket. I guess I should have used a CAB lacquer, but I have never had an issue with discoloring before.
Forum Responses
(Finishing Forum)
From contributor B:
What was the primer tinted with?
From contributor D:
Right, you should've used a non-yellowing finish. Exposure to light speeds up the yellowing process of a precat. Nitrocellulose lacquers yellow as they age.
From the original questioner:
The primer came white. This is not a UV process. The fronts of the doors are not yellowing, just the backs. Opticlear is not a n/c lacquer.
From contributor P:
Some alkyds yellow in the presence of light and some yellow in the absence of light. Pre-cat lacquers contain nitrocellulose as well as some amount of crosslinking resins to make them more durable; and alkyds are commonly used. Like contributor D said, you'll need to use a non-yellowing finish to avoid the problem.
From the original questioner:
I'm told that Opticlear is not a "tint-ready" product, but it can be tinted with 844 pigments. It seems that it is the topcoat (clear scuff-coat) that yellowed (in a few months), but only on the back sides or where it was in a dark place.
From contributor P:
A closed cabinet still has air (oxygen) in it. Pre-cat lacquers often contain alkyds to give them the extra durability. Some alkyds will turn yellow when they're not exposed to light (e.g., the backside of a cabinet door).
The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).
Comment from contributor A:
Yellowing in the dark can be affected by the type and amount (referred to as length) of oil. Long oil alkyds have the most oil and short oil alkyds have the least. The type of oil can be important. Most alkyds are presently made with either soya or tall oil, unless they're specialty products. Tall oil yellows less than soya oil. So, ideally you would want a tall short oil alkyd (yes tall short is correct!). The retailer will have no idea of the type of oil and its length but the paint manufacturer might supply that information through their lab if you insist. Note that most alkyd house paints are either long or medium oil, so short oil may be hard to find but they still apply like an alkyd. If formulated properly, you'll hardly know the difference.
