Jason Henderson, of Kaikoura Suburban School, asks :-

What is the colour of paint made out of?

Dimitri Christoforou, a paint chemist with Resene Paints Ltd of Lower Hutt, responded.

White light is a mixture of different colours that are separated and observed in a rainbow. Some substances reflect all the light falling on them and therefore appear white. Others absorb all the light and appear black. But many substances reflect some of the light falling on them and absorb the rest. For example, a red object reflects red light and absorbs the remaining colours. A purple object reflects red and blue but absorbs yellow and green light.

Paints consist of three main substances: binders, pigments and solvents. Binders are a tough plastic-like material that gives paint strength and holds it together. Binders are usually transparent and so dont absorb light, but allow it to pass tbrough. An example is varnish, which allows us to see the surface underneath.

Pigments are coloured powders that are dispersed (well mixed) in the binder. These are what absorb or reflect the light thus colouring the paint and preventing us from seeing the surface underneath.

Solvents, such as water or turpentine, make the paint runny and easy to apply, but evaporate afterwards to allow the paint to become hard and tough.

Diffent powders (pigments) absorb and reflect different colours of the visible spectrum, which means that they are seen as having different colours. By selecting the right pigment or combination of pigments we can formulate any desired colour of paint. Because paints are available in thousands of different colours, it is easier to add the desired pigment at the end in the form of a concentrated pigment paste, whioh is done at the shop when the customer orders the colour he or she wants.

The first pigments used by ancient people were naturally occurring minerals that were ground up and used for cave paintings. Volcanic red ochre is one. Modern pigments are manufactured to allow for minimum colour variation and have excellent resistance to fading. Titanium oxide is used for white, chrome oxide for green and different types of iron oxide for red and yellow.