Blue makes white! A lesson in colours.

Optically speaking, ultramarine blue is the opposite of mid-yellow - the shade that old ‘whites’ take on with age. In this way it removes the yellow you don’t want and turns it into white. Together with this comes another effect, this time from physics – ultramarine is an ultra-violet-ray absorbent: it takes up UV rays and returns them as visible light. Result: your whites recover their pristine whiteness. All you have to do is add a packet of ultramarine blue to the washpowder.