Posted by on Jun 7, 2011 in Interesting Facts | 2 comments

Artists and painters have it good. They can fulfill their imagination with all the colours they could ever want. But it wasn’t always so.

Ancient cave paintings were pretty well limited to dark browns and reds, making use of rusted iron or earth. Bright blue and purple have become associated with royalty because, up until a three hundred years ago, those colours were very rare and expensive.

You see, colour is a matter of chemistry so the artists had to wait for the scientists to get some things figured out. Let’s look at how colour works.

You know that white light is actually a mix of all the colours of the rainbow. All those colours are tucked inside the sunbeam. When that sunlight hits your white painted windowsill, every colour gets reflected. The light that bounces off the paint and into your eyeball appears white.

That same white sunlight hits your blue wall. The reason the reflected light appears blue is because the paint on the wall is actually absorbing all the other colours of the light. Red, orange, yellow, green, indigo, violet, and all the colours in-between get trapped in the paint… except that which makes up the blue colour you see.

A black object would be absorbing nearly all of the light. The fact that this light energy is being absorbed can be felt on a sunny day. Place a black sheet of paper beside a sheet of white paper. Before long you can feel the difference in heat.

A pigment is the particle that is picking and choosing the wavelengths of light to absorb or reflect.

Now, a paint factory can’t just go and create the different pigments for each colour. They have to make their plain paint base first, then find the right ingredient to add colour. I’ve already written about white paint, and how it used to get its white pigment from flaked lead. For health reasons, modern white pigments are extracted from zinc or titanium.

Most paints are simply a fine powdered pigment that is suspended in some sort of goop such as oil, latex or, once upon a time, egg whites. The powdered pigments must be taken from somewhere, be it an organic source like flowers and minerals, or through advanced labratory chemistry which led to the “discovery” of new colours.

The pigment Prussian blue, chemically known as Ferric hexacyanoferrate, was discovered by accident. It was the first synthetic alternative to the very expensive Ultramarine blue, made from a semi-precious gem. The Prussian blue compound has also been used as an antidote for heavy-metal poisoning. Oddly enough, part of the pigment is made from cyanide, but it is tightly bound in the chemical composition so as to not be toxic.

As the chemistry of a pigment changes, so does the colour. Most commonly seen in the process of oxidization (rusting) such as a cut apple turning brown. The prized pigments are not only vivid in colour, but chemically stable so masterpieces can survive for the future.