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Reading Selection, Lesson 16

Mixing Colorful Coverings

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Wouldn't the world be a dull place if there were no such thing as paint? Since prehistoric times, paints have been used in art. The earliest cave paintings were made using paints derived from colored soils and rocks or from animals and plants. These were mixed with other substances, such as egg white, which allowed the pigments to spread over and stick to the surface being painted. Today, paints are used to protect and decorate surfaces. They are carefully formulated mixtures, designed to do specific jobs, and are available in a seemingly infinite variety of colors. Let's examine these mixtures more closely and see how the different properties of the substances from which they are made work together.

Bhimbetka rock painting

Throughout history, artists have used a wide variety of pigments in their paintings. Many paints contain oxides of metals, which provide color. Artists working in what is now Bhimbetka, India painted these images. Many modern oil paints contain metal oxides that produce the vivid colors associated with oil paintings.

Most paints consist of pigments, a vehicle, and a solvent, plus other additives that perform a variety of functions. Pigments give the paint color and also make it opaque (not transparent). The type of pigment used depends on the color of the paint wanted. For example, white paint often contains the pigment titanium dioxide. However, several pigments can be used together in varying quantities to produce a wide range of paint colors. For instance, even though titanium dioxide is used to make white paint, other pigments are often mixed with it to produce paints of other colors. For example, titanium dioxide is mixed with barium chromate or cadmium sulfide to make yellow paints, with chromium oxide to make green paints, and with ultramarine or dyes such as indathrone blue to make blue paints. In addition to adding color to paint, titanium dioxide has the ability to hide the surface that is being painted. For this reason it is called a hiding pigment.

Vincent Van Gogh's <em>Sunflowers</em>

Van Gogh used bright yellows in many of his paintings (including Still Life: Vase with Twelve Sunflowers, shown here). A lead chromate pigment provides the yellow color.

Paint must also contain a substance that will make the pigment stick to the surface being painted (like the egg white used by prehistoric cave painters). These bonding substances are called the vehicle. They are usually made from plastic-like substances which, when dry, form a hard, flexible protective coating.

Solvent thins the paint and helps it spread during painting. Mineral spirits are used as solvents in some glossy paints. These dissolve the vehicle. When the paint dries, a hard film is left behind. Many emulsion paints and modern latex paints use water as a thinner, although in these cases, the water does not dissolve the vehicle but keeps it finely divided. When the paint dries, the finely divided emulsion comes together to form a hard, flexible surface.

Paints often contain a variety of additives that perform various functions. They may improve the weather resistance of the paint, affect the way the pigment is dispersed to produce special finishes, or speed up the drying process.

An artist painting a mural

This artist is painting a mural. Artists' paints contain many different solvents. Water and turpentine are the most common.

 

 

 

 

 

 

 

People painting a design on a barn

Paint is a complex mixture designed to be applied as a liquid and to dry into a decorative and hard, but flexible, protective finish.

QUESTION

Advances in technology have given us easy and affordable access to full-color printers—ink jet, bubble jet, and laser. Conduct research on one of these types of printers to find out how it uses pigment in doing its job.

 

 

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