Mad About Science: Paint

By Ben Olson
Reader Staff

As the weather turns warmer, more of us are out there working on projects that might involve paint. Have you ever stopped and thought about what exactly paint is and why we use it? Have no fear, that’s exactly the topic for this week’s column.

There is a certain freshness that a new coat of paint provides. It can turn a dreary room into your favorite space, or make an old car look like it just came off the line. But paint is more than just fancy color, it’s actually protection from the elements. We paint metal to keep it from rusting or wood to prevent rotting. Think of paint as a skin you’re placing over your car, fence, house or boat that helps protect the vital organs inside.

Humans have used some form of semi-permanent markings to memorialize their lives since at least the Stone Age. The earliest “paint” supplies found were abalone shells full of ground ochre and charcoal, used in the Blombos Cave in South Africa, which are dated to be around 100,000 years old. Unfortunately no paintings were found in this cave, just the supplies. To see the first images still evident on cave walls we must travel to about 44,000 years ago when individuals in Europe, Australia and Indonesia painted images of hunters and herders on cave walls, expanding the color palette considerably.

Paints then, and now, are all basically made up of three components called the pigment, the binder and the solvent.

Pigments used in prehistoric times included blood, sap, berry juices, dried plants and roots, and minerals. Artists would mix their pigments into paint using water, saliva, urine or animal fats, then apply them with fingers, brushes or by blowing them through hollow bones.

Ancient Egyptians advanced the medium considerably by mixing paints with binding agents like egg and began painting on plaster. Greeks and Romans expanded on these techniques until the Renaissance, when Italian artists painted with plant oils to create works containing a wide spectrum of color and depth that still wow museum-goers to this day.

“Modern” premixed paints didn’t evolve until the mid-19th century, when Shermin-Williams sold the first premixed wall paints in 1867. Before that, people had to mix their own wall paint from powdered pigments.

Since the 1940s, paint has advanced to produce the right type for the right job. Synthetic pigments were introduced, leading to easier preparation for artists and house painters, expanding the once mineral-based limited color palette to any color you could imagine.

Paints today stick to the same formula of pigment, binder and solvents. Pigments are, of course, the color of the paint. A specific color is produced because the pigment reflects some wavelengths of light and absorbs others. Traditionally, metal compounds have been used to produce certain colors. Titanium dioxide — a bright white chemical often found in sand — is used to make white paint. Iron oxide — or rust — makes yellow, red, brown or orange paint. Greens were more difficult to produce, with some using verdigris or ground malachite. Blue pigments were introduced by the Egyptians, who mixed ground limestone with sand and a copper-containing mineral such as azurite, which made an opaque blue glass that had to be crushed and combined with thickening agents to create a glaze. Black hues are made from carbon particles, and so on.

Because pigments are usually solids, they won’t bind to a surface by themselves, so a binder additive is needed. A binder’s job is to glue the pigment particles to one another, but also to make them stick to the surface that’s being painted. Some binders are made from natural oils like linseed oil, but most modern paints use synthetic plastic binders, such as latex.

Mixing pigment and a binder only makes a thick substance that’s difficult to spread. By adding the third component — a solvent — paints are made thinner and flow more like a liquid, which helps to spread the paint evenly. Once the paint spreads out, the solvent evaporates into the air, leaving the paint evenly applied and dry beneath it. Paints that use water as a solvent are easy to clean up if you spill them, and don’t smell so much like chemicals. Oil-based and glossy paints use solvents made from strong organic chemicals extracted from petroleum. If you find an old can of oil-based paint, you will recognize the solvent as the thin fluid sitting on top of the pigment. That’s why it’s important to mix paint well and often — the three components like to separate if left idle.

Next time your honey-do list includes painting the fence, take a moment to think of how far we’ve come, going from ground ochre in abalone shells to paints that glow in the dark.

Stay curious, 7B.