How Does Colour Stay in Cloth?

Step 1 of 5

Colour is about which light comes back.

A dye molecule absorbs some colours of light and lets the rest bounce off. Red cloth is red because the dye is swallowing everything except the red, which reaches your eye.

Step 2 of 5

A dye has to grab the fibre.

If the colour only sits on the surface it washes off in one go. A real dye forms a bond with the fibre molecules, so the colour is held on rather than resting there.

Step 3 of 5

Some dyes need a go-between.

Many natural dyes will not stick to cloth at all on their own. Soaking the cloth first in a metal salt gives the dye something to grab, with the metal holding both — and it changes the shade too.

Step 4 of 5

Colours used to be rare and expensive.

Every dye once came from a plant, an insect or a shellfish. Deep purple took thousands of sea snails per garment, which is exactly why purple meant royalty for a thousand years.

Step 5 of 5

Sunlight slowly takes it apart.

Light carries enough energy to break dye molecules. Once broken, a molecule no longer absorbs its colour — which is why a curtain fades on the side facing the window and not the other.

The first made dye was discovered by accident by an eighteen-year-old trying to make a malaria medicine. He got a purple sludge instead, and started an industry.