The Golden State: Where & How to Live, Secure, Visit, Enjoy and Thrive in California
Coloring Finishing And Painting Wood
The need for an aging process is said to depend somewhat on the type of driers used in the varnish. The use of some of the new "non-sludging" driers is said to have made aging of less importance.
334. Ingredients in Varnishes.—The formulas for varnish-making that are being used in manufacturing our present-day varnishes are considerably different from tliose used with fossil resins or even ester-gum only a dozen or fifteen years ago.
The ingredients selected for the manufacture of the new synthetic varnishes, tho somewhat different from those used just a few years ago, come under the same general classification; namely, (1) resins, (2) drying-oils or vehicle, (3) solvents or volatile oils, and (4) driers. The real composition of the new varnishes is much different from the old, however, because of great differences in most of the classes.
Synthetic resins, described in another chapter in this book, are now used for making the quick-drying varnishes. The slow-drying varnishes are made of fossil gums, estergum, and limed rosin. Many varnishes contain a mixture of resins. Sometimes fossil gums are added to the solution containing molten synthetic resins or ester-gum in order to produce certain types of varnish films.
The drying-oil or vehicle has gradually been changed from linseed-oil formerly used in all varnishes to Chinawood oil, also called tung oil, which requires special treatment but which possesses valuable and quite different qualities from those found in linseed-oil.
It is from the inclusion of synthetic resins and Chinawood oil that the new quick-drying varnishes obtain the peculiar drying principle known as polymerization, which causes rapid setting and a reaction thru the film something like that of the formation of a jelly.
Turpentine, the solvent and thinner formerly placed in the fossil varnishes of a few years ago, has been mostly replaced by xylol and cheap mineral thinners, such as varnolene and other similar solvents which are petroleum products. Turpentine is known to be a more active oxygen carrier than are the petroleum thinners; but its cost is usually four or five times as much, and it leaves very little valuable residue after evaporation. Turpentine causes the varnish oils to flow and spread easier under a brush because it evaporates more slowly than do the substitute oils. The lack of turpentine seems to be the cause of the stiff brushing or pull that is noticeable when applying synthetic varnishes.
