Why Do Paintings Last Forever — or Fade Away?

Paintings stay fresh or fade depending on what they're made with. If a painting uses strong, tough colors like red from iron, it stays bright for a long time, kind of like how chocolate lasts longer than ice cream. But if the paint is made with weak colors that break down easily, like blue from lapis lazuli, it can lose its color over time, like how lemon juice makes paper yellow.