Benzine is also used for diluting paint, and dries by evaporation without residue.
Driers are oxidizing agents introduced into paint to promote rapidity of drying. They are usually salts of lead or salts of manganese. In this country they are ordinarily found in liquid form, but in England paste driers are usually employed.
Allowance for Drying. One of the most im portant things needed to secure a durable job of painting is that sufficient time should be allowed to elapse between coats to insure the under layer of paint being perfectly dry before another layer is applied. This does not mean mere sur face drying; it does not mean that the paint shall not come off when touched by the finger; but that the paint film or layer should be dry throughout the entire thickness. Paint does not dry by evaporation, but largely by oxidation. The linseed oil used as the vehicle takes up oxy gen from the air, and forms a tough, leather-like, gummy compound called "linoxyn." It is this gum which gives linseed-oil paint its waterproof qualities. If turpentine, benzine, or other vola tile liquids are used in the paint in order to make it work easier or to hasten its drying, these evaporate, leaving only a little oil and turpen tine to act as a binder for holding the particles of pigment together and causing them to cling to the wood. In order to hasten drying, it is the custom to add certain oxidizing agents which exert a chemical action upon the linseed oil; but while these cause more rapid drying, they also introduce a destructive agency, and paint that is made to dry quickly by means of these driers is also quick to perish. This is another reason why the work of painting should not be hurried.
Blistering and its Causes. One of the great est causes for complaint, especially about paint ing clone in summer time, is blistering. Some times the trouble may be traced to inferior paint, at other times to wrong application of the paint; but still oftener it may be traced to moisture back of the paint. Of course, the hot summer sun is apt to aggravate these causes, and it is a fact that blisters are not so likely to occur on the north side of a house as on the faces that are exposed to the direct rays of the sun. An
ocher priming coat, especially one composed of the cheap American ochers sold as "priming ochers," is very apt to cause blistering in sub sequent coats, especially if the priming coat is not given several weeks to dry. This is because these cheap ochers, being largely clay, absorb and hold moisture, which turns into steam and raises the outer paint skin. Unfortunately, many painters seem to think that anything is good enough for priming, whereas this first coat is just as important as the foundation of a house, and, unless it is made of the best materials and applied in a thoroughly workmanlike manner, the whole subsequent paint structure will be unreliable. If cheap and inferior materials are to be used on any portion of the work, it would be far preferable to use them on the last coat rather than on the priming.
Most Satisfactory Priming Coat. The best white lead mixed with raw linseed oil and enough turpentine to insure the penetration of the paint particles into the pores of the wood and make the paint dry flat and hard, is the most satisfactory priming coat. Enough lampblack, not more than one or two per cent at most, should be added to make the priming coat a light lead color. This will cover up the stains and discolorations so common to modern lumber, and will make the subsequent coats of paint cover better. This is even more necessary if the house is to be painted white than if colors are to be used. For use under any strong, dark color, the priming coat may be tinted with the same color instead of with lampblack. One of the most important things in connection with the priming, and, in fact, with any painting done in mid summer, is that it should be thoroughly brushed out and rubbed well into the wood. On no account should heavy coats of paint be used in summer time, as blistering will almost surely occur.