The Golden State: Where & How to Live, Secure, Visit, Enjoy and Thrive in California
First Aid For The Ailing Houses
PAINT MATERIALS
In drying, paint forms a tough film that attaches itself to a surface by hardening in its pores. In oil paints, this film forms through the effect of air on the oil: the oil becomes oxidized. With water paints, the result is obtained by a drying and hardening of the ingredients as the water evaporates.
When some kinds of oil are exposed to air, they evaporate and disappear; for example, turpentine and gasoline. With lubricating oil, nothing much happens; it is supposed to remain greasy. The kind of oil that is used in paint will thicken and become gummy. Several kinds of oil, called drying oils, will act in this way; the one which, for abundance and low price, is in most general use is Unseed oil. Recently, however, there has been increased use of other oils besides linseed; one of the most popular is soybean oil.
Many of the new paints do not use an oil at all; their vehicle is some form of synthetic resin. Most popular of the synthetic resins is latex, used in a water-emulsion flat interior paint. Other paints of the same type use vinyl bases. In the synthetic-resin enamels, alkyd resins provide tough, almost impervious films combined with extremely high gloss. Acrylic resins are also used for this type of coating.
Oil paints and the newer resins which are solvent-based, have the vehicle as the principle ingredient. Another part of the liquid is turpentine or mineral spirits, which helps the vehicle to penetrate the pores of the surface and makes the paint flow smoothly from the brush. In drying, the turpentine or mineral spirits evaporates completely. There may also be a small proportion of a liquid dryer (such as "japan"), which quickens drying and hardening.
Water paints and water-emulsion paints use water as the solvent. The vehicle is a water-suspended material that will harden and dry in the surface as the water evaporates.
The solid part of paint, which makes it opaque and gives it body, may be lead, zinc, titanium, or other metal in chemical form. Lead is still used widely in the form of a white powder; it is mixed into a paste with Unseed oil to make paint. These metals are the pigment in the paint; less expensive house paints still use an exclusively lead pigment.
Zinc and titanium in several forms can be used alone but are likely to be combined with white lead. Titanium has great hiding power and is generally used in high-grade outdoor white paints.
Paints may also contain extenders that give the formula greater body and increase hardness. Mica and barium compounds are often used for this purpose.
