Why Do Oil Paintings Yellow Over Time?

Imagine you have a clear glass jar filled with sparkling water. If you leave it open for years, the water might turn slightly cloudy or brownish because of the air. Paintings made with oil paint do something similar but much slower.

Long ago, artists used special oils like linseed oil to mix their colors. Over time, this oil changes when it meets light and air. It gets thicker and darker, turning from clear to a warm honey color. This is called aging.

If the paint layer becomes too thick or if there are too many old layers of varnish on top, the whole picture looks like it has a brown blanket over it. Dark shadows appear where there should be bright whites, and blues can look a bit grayish. This is why old paintings sometimes look different than when they were first painted!