Wanda: 
  Probably this is a combination between your lab environment and the type/quality of the paint used.
  Try first to find out the type of paint used and if it is of the alkyd type. White alkid wall paints become yellowish when there is not enough light and also in the presence of ammonia and chlorine.
  Try to find out the amount of light in your lab and note if yellowing is more acute in the less exposed to light areas. Sometimes ammonia is used as a "sectioning helper" of hard blocks and chlorine is sometimes used to clean/disinfect counter surfaces.
  A combination of all these factors can be the cause for your wall yellowing.
  Hope this will help you.
  René J.

Smith Wanda  wrote:
  Good Morning Netters,
As much as I hate to admit this...the walls in my lab where the tissue processors, embedding center, UPS for the embedding center, and microtomes are, they are turning yellow. It has been happening gradually, however now when the histotechs wipe the counters each day, the paper towel is yellow. It almost looks like nicotine tar, but they assure me they are not smoking in there in the mornings!!!
My lab is 3 years old and they designed it with adequate ventilation to remove fumes, but I'm at a loss on this one. Please help!!!!!
Wanda

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