Nathan Bartlett, age 13, of Chester, Pa., for his question:
WHAT IS USED TO MAKE PAINT?
Paint is a mixture of a liquid and one or more colored powders. The colored powder is called pigment and it gives the paint its color. The liquid that carries the pigment and makes the paint easy to spread is called a vehicle, or "binder," and it may include a solvent or thinner.
Nine kinds of paint are commonly used and they include oil based paints, latex paints, lacquers, fire retardant paints, heat resistant paints, cement water paints, metallic paints, wood and plaster primers and enamels.
Oil based paints often have a vehicle made of vegetable drying oils, such as linseed oil or soybean oil. Zinc oxide, titanium dioxide and iron oxides are the most widely used prime pigments in oil based paints.
Latex paints are water thinned. Many prefer latex paints to oil based paints for household painting because they are easier to use. Brushes, rollers and other equipment can be easily cleaned with soap and water after latex paints are used.
Wall paints of latex are made from polyvinyl latex vehicles and contain prime and inert pigments. Masonry paints are made with polyvinyl acetate or acrylic emulsions and are also water thinned. They contain both prime and inert pigments. Outside latex have polycrylic latex vehicles.
A lacquer consists of a solution of synthetic resins and fast evaporating organic solvents. Prime pigments are dispersed in the solution to give color.
Fire retardant paints have prime pigments and either oil or oil resin vehicles.
Heat resisting paints contain vehicles with silicone resin.
Low pigment content makes enamels dry with a high gloss or shine. Most enamels have varnish or alkyd vehicles and are solvent thinned.
The paint maker puts a small amount of the vehicle into a large mechanical mixer at the paint plant and gradually adds the powdered pigment. The slowly rotating blades of the mixer make a heavy paste out of the pigment and vehicle.
In a paint making plant, a worker next puts the paste into a mill or grinder to break up the pigment particles and scatter them throughout the vehicle. Ball or pebble mills are large, steel lined cylinders that contain pebbles or steel balls. As the cylinders rotate, the balls or pebbles spin and hit against each other, grinding the paint. A roller mill has steel cylinders that rotate against each other to grind and mix the pigment.
Another worker then pours the ground paste into a tank where it is mechanically mixed with more vehicle, solvents and driers.
A worker next adds a small amount of pigment to give the paint the exact color and shade desired. This worker is called a "tinter."
Finally the paint is strained through a felt bag, or some other type of filter, to remove any solid bits of dust or dirt. Then it it is poured into a filling tank and finally into the metal cans in which it is sold.