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Coloring Finishing And Painting Wood
Varnish Evolution
318. Importance of Synthetic Resins.—Important steps forward in science and the making of new products valuable to man have characterized the last quarter century. Various fields of human activity have contributed offerings of utility; among those of very great need and value being the resin-like materials which have been discovered and perfected in the laboratories of the chemists. The uses of these new resins, often resembling amber in appearance, are now in the thousands, and their value is beyond that of the fondest dreams of the research workers of a few years ago. These purely synthetic materials are widely used for molding plastics, for various laminated objects, for valuable cements; for coatings for fabrics, for telephone fixtures, for numerous automobile parts; and for a thousand other purposes, among which are new, much needed resins for the varnish-maker to replace old fossil resins which are rapidly becoming scarce. Synthetic resins add a new and unheard-of speed to the setting of the so-called four-hour varnishes, in addition to decreasing the time needed for the hardening of coatings made from such varnishes.
One large manufacturer of synthetic resins has stated that greater improvements in surface coatings have appeared during the past 2.") years than during the previous century. Formulas for making varnishes were considered to be of great value and were kept secret until the new synthetic resins appeared and the trained chemist took over the manufacture of varnishes. Today, a scientist who is a specialist in physical and colloidal chemistry, is at the head of an experimental laboratory where all formulas are tried out. Many manufacturers of synthetic resins publish suggestive varnish formulas for the use of varnish-makers, and such formulas are available to almost any one who is interested. A varnish formula is probably of much less importance than when the old fossil resins and linseed-oil were used, because great changes in the final product turned out can be brought about by variations in the heat treatments of the synthetic resins and oils used in varnish manufacture of the new quick-drying type of finishes. Details of procedure in the varnish kettle are more likely to be kept secret by manufacturers than any listing of proportions of ingredients such as are found in a varnish formula.
319. Classes of Varnish.—Two classes of varnish are mentioned in Sec. 175, "Classification of Varnishes,"p. 216. Today, some ten or twelve years after this classification was made, there seem to be four rather distinct classes. The types are distinguished by evaporation of the thinners and solvents and the method of hardening of the films made from the varnishes. The four classes might be named as follows: (1) spirit-varnishes; (2) linseed-oil-fossil-gum varnishes; (3) China-wood oil with fossil-gum varnishes; and (4) synthetic-resin varnishes.
