Hardwood Finishing

A good. paint should meet, the following requirements: First, it should spread readily—or, in other words, it should be capable of being spread out in a thin film over a large area, with comparatively little muscular exertion. On a good surface, a gallon of paint should spread over an area of from 700 to 800 square feet, one coat ; or should cover from 350 to 500 square feet, two coats.

Second, it should cover well. By the covering capacity of paint is meant its ability to hide the surface to which it is applied. A paint may have the maximum of spread ing capacity, yet cover very poorly. For example, a mix ture of whiting and oil has a fairly good spreading capa city, yet, when applied upon a board in one, two, or even three coats, the wood will not be hidden in the slightest. The same is true of barytes and oil, and also of ground silex and oil, yet all these three substances are frequently used as constituents of mixed paints. In such eases their lack of capacity is counterbalanced by the admixture of some pigment of great covering quality.

Again, the paint should adhere well to metal or wood when mixed with pure raw linseed oil and spread on in the form of a film. The pigment should be ground exceed ingly fine, so that it will remain in suspension in the oil and not settle to the bottom of the pot. This is essential, as otherwise the coating would lack uniformity. The paint film should have sufficient elasticity to expand and contract with the wood or metal to which it is applied, without peeling or flaking off. It should be fairly durable. It is expected that any outside paint will in time require renewal, but a good paint should have a reasonably long life. When renewal is required the paint surface should be in such a condition that no expensive burning off, scraping, or other special preparation should be required. No paint is economical if it lasts five or six years and then perishes in such a way that the old paint requires to be burned or scraped off before repainting is possible. True paint economy is determined, not by first cost nor even by the durability of the first painting; it is measured by the cost of keeping the house in good condition for a series of years.

White lead spreads readily and possesses the maximum covering capacity of any white pig ment. When the color of the paint is modified by dark pigments this is not so great an advan tage as when the work is to be finished in white. It perishes by chalking or powdering; and when the white lead is not well made (for example, if there is an excess of acetic acid left in it after corrosion), this chalking occurs within a com paratively short time. The fact that white lead

perishes by chalking makes it very easy to re paint, needing only dusting off to fit it for a new coat, the oil from which will unite with the pow dered lead on the surface and closely bind the new coat of paint to the old surface. White lead darkens by exposure to sulphur fumes or to gases containing sulphuretted hydrogen, but this is a negligible quality in exterior painting, except in the neighborhood of sulphuric acid works or coke ovens.

Zinc white spreads much further than white lead, but has less covering power. It perishes by cracking, followed by flaking and peeling from the surface. As a rule, zinc paint will last longer than white lead.

In general it may be said that white lead is too soft to form a durable paint, and zinc white is too hard and brittle. Manufacturers of the best mixed paints combine the two pigments, and upon the proper proportioning of the two will depend the maximum durability and econ omy of the paint. A mixed paint must be judged by two things—first, by its average life, or the length of time which experience has shown it will require before renewal; and, second, by the manner of its perishing. If the manufacturer has succeeded in producing a paint which will powder, or at any rate flake off in such minute particles as practically to powder or chalk, then it is safe to use and will probably prove to be economical, but if it peels in large flakes, then it is well to let it severely alone.

The trouble with many mixed paints is that the proportion of zinc white is too large to ob tain the best results, the object of the excessive proportion of zinc white being to prevent the "fatty" degeneration characteristic of pure white lead and linseed oil paint. Very good re sults are obtained by mixing with the last coat of paint about ten to fifteen per cent of French zinc white. This hardens the paint and corrects the tendency to excessive chalking, while at the same time there is not enough zinc white to cause flaking. By "French" zinc white is not necessarily meant zinc white that is made in France, but that which is made from the metal zinc or spelter. The cheaper American zinc used by mixed paint manufacturers is made direct from the zinc ores.