What Is Paint Made Of?
The history of paint goes back about 100,000 years. From that time to the present, people have found amazing sources for pigments.
“Indian yellow” was the dried urine of cows fed a diet of mango leaves. “Mummy brown” came from — you guessed it — ground-up Egyptian mummies. Right up through medieval times, many people believed deep red “dragon’s blood” actually came from dragons. It didn’t. It came from the sap of the Dragon Blood tree (Dracaena cinnabari).
Pigments are just one component of what we call architectural paint, basically any type you can spray or apply with a paintbrush. This type of ready-mixed paint dates to the 1800s, making it much newer than the paints artists use. It must be durable as well as colorful, and manufacturers must reproduce any batch they make to guarantee color and quality uniformity.
Today, many paint products flood the market, and some are definitely better than others. Paint chemistry can be a complicated topic, even for an ex-pro painter like myself. But anyone who shops for and uses paint should have a grasp of the basics.
What Is Paint Made Of?
Every can of paint contains three essential ingredients: a binder, pigments and a solvent. Manufacturers sometimes refer to the binders and solvent collectively as the “vehicle” for the pigments, which supply the color.
Binders
Paint binders are polymer resins, i.e. compounds with long strings of molecules that join to form a hard yet flexible film. Early paint manufacturers exclusively used alkyd polymers derived from plants, like boiled linseed oil. But modern binders are mostly synthetic materials like acrylic, urethane or epoxy.
When exposed to air or a catalyst, the molecules in polymer compounds cross-link by forming permanent, strong bonds with each other in a process called curing. That turns paint hard, and it’s irreversible, which is why you can’t soften paint after it cures.
Drying vs. curing: Paint dries when all the solvent evaporates. But dried paint hasn’t necessarily cured, because it usually takes longer for all the molecules in the binder to cross-link. Depending on the product, curing can take several hours to several weeks.
Pigments
Old-world paints almost all used organic pigments like Indian yellow, dragon’s blood and many more, but modern pigments are mostly inorganic. They’re essentially ground-up minerals and mineral salts. Some of the most common include:
- Titanium dioxide: Also known as titanium white, it makes paint white and brightens paints with other colors.
- Carbon black: Makes paint black and darkens colors of other hues.
- Iron oxides: Make earth tones like red-tinged sienna and yellow-tinged ocher.
- Chromium compounds: Make yellows, oranges and greens.
- Iron blue: Aka Prussian blue, it gets its vibrant color from a reaction between iron and cyanide in water.
In making paint, manufacturers dissolve the pigments in a solvent to help them spread uniformly throughout the mixture.
Solvents
The solvent turns paint into a liquid so you can spread it or spray it. These days, water is the most common paint solvent. Manufacturers use it to make latex and acrylic latex paint.
If you’re using an “oil-based” paint, the solvent is probably turpentine (also called white spirit), derived from pine sap.
Other chemicals may be mixed into the solvent for oil-based paint, including methyl ethyl ketone (MEK), xylene, toluene, alcohol and acetone. All are toxic and high in volatile organic compounds (VOCs), and California and other states prohibit the sale of paints that contain them for use indoors.
Two Important Paint Ratios
It isn’t simply the ingredients that make a good paint, but the relative amount of each. When shopping for paint, look for these two ratios on the can or in the company literature.
Volume solids (VS): The ratio of the volume of solid material in the paint to the total volume of the paint, multiplied by 100. Generally speaking, the higher the VS ratio, the better the product.
Pigment volume concentration (PVC): The ratio of pigments to binder. A higher number indicates a higher volume of pigments, which makes for good hiding and color vibrancy, but poor wearability.
Interior flat wall and ceiling paints usually have a high PVC, making them difficult to clean because the color can rub off. Exterior paints and interior enamels, on the other hand, usually have a low PVC and a high binder concentration. That makes them more durable and easier to clean, but somewhat less vibrant.
Other Ingredients
Besides the three essential ingredients, paint manufacturers often include additives that take up a small percentage of total volume. If they aren’t already in the paint you’re using, you can often add them yourself.
- Bactericides, fungicides and algaecides: Protect the paint finish from deterioration caused by microorganisms. Zinc oxide is a common additive for this purpose.
- Driers: Make the paint dry faster.
- Dispersants, soaps and surfactants: These separate the pigment particles for better color uniformity.
- Thickening and anti-settling agents: These keep pigments uniformly dispersed and minimize shaking and stirring.
- Silicone: Improves weather resistance.
- Sheen control additives: Things like diatomaceous silica, calcium carbonate or clay.
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