by waaytoomuchintothis » Sun Sep 09, 2012 1:14 pm
When white turns slightly yellow without coating, there is a vapor or fume in the air where it cured. When contractors paint a wall white in a building, they have to schedule the painting for after the sheet rock guys are gone and the mud is fully cured, because the white paint will turn an uneven creamy off white when the fumes are present. Latex paints and oils will have similar types of cautions. I should also say that it isn't just white that will turn in the presence of fumes that it is allergic to. They all do, you just can't see it. All kinds of fumes do things to paint, smoke, ammonia, lemon juice, bug spray, ozone from electric motors, vinegar, even other paints. You need good ventilation anyway, and that's the best to isolate the paint while it cures.
When it turns after coating, one of two things has happened: Either the coating went on too soon while the paint is still "gassing out", or the coating itself has yellowed, which isn't usually the case, because as soon as you put it on, you would see it. Future will get cloudy and slightly yellow if the bottle is left unsealed too long, but you would see that before using it. Over a period of many years, Future will get yellow, but its more like a gold, a dark yellow. Then you carefully wipe down the white surfaces with a dilute ammonia solution, then thoroughly clean with water. When completely dry and no trace of ammonia left, you can recoat like new.