Why Finishes Yellow
Most finishing resins yellow over time and nitrocellulose lacquer and oil-based polyurethane are two of the worst. The reason they do this is because of exposure to light and air.
How do you fix yellowing lacquer?
Yellowed Lacquer -- Quick Fix
When the finish has other defects that detract from the appearance of the piece, you can sometimes fix them and lighten the yellowing by scuffing the old finish with 220-grit sandpaper and spraying on a new coat.
Why does my clear coat turn yellow?
Yellowing of clearcoats is a natural phenomenon during weathering processes, as well as from extreme baking conditions, due to polymer degradation. However, occasionally yellowing may be caused by unexpected chemical reactions occurring in the clearcoat.
