Why Do Oil Paintings Yellow Over Time?

Imagine your favorite white t-shirt getting a little dusty and tan after being in the sun for years. Paintings do something similar, but much slower. Most paintings use oil from flax plants to hold their colors together. This oil acts like a natural glue.

The most common problem happens with white paint. Artists often used a special powder called lead white because it is so bright and opaque. But this powder loves oxygen. Over decades or centuries, the oxygen attaches to the lead, turning the bright white into a creamy yellow color. It is like watching ice cream slowly melt.

Paintings also have a sticky layer on top called varnish. Think of it as clear nail polish protecting your nails. Old varnish gets dirty and yellows too. When you clean a painting, conservators remove this old yellow layer to reveal the crisp colors underneath. So, when you see an old museum piece looking warm and cozy instead of bright and cool, it is just the paint growing up gracefully.