Scientific American 16, 30.12.1854
Having received a number of letters recently, inquiring how to make different kinds of varnishes, we present the following, to save time in replying to each separately.
Different substances are employed for making varnish, the object being to produce a liquid easily applied to the surface of cloth, paper, or metal, which, when dry, will protect it with a fine skin. Gums and resins are the substances employed for making varnish; they are dissolved wither in turpentine, alcohol, or oil, in a close stone-ware, glass, or metal vessel, exposed to a low heat, as the case may require, or cold. The alcohol or turpentine dissolves the gum or resin, and holds them in solution, and after the application of the varnish - this mixture being mechanical - the moisture of the liquid evaporates, and the gum adheres to the article to which it is applied.
White Spirit Varnish. - Sandarach, 250 parts; mastic in tears, 61; elemi resin, 32; turpentine 64; alcohol, of 85 per cent., 1000 parts; by measure.
The turpentine is to be added after the redins are dissolved. This is a brilliant varnish, but not so hard as to bear polishing.
Varnish for Certain Parts of Carriages.
- Sandarach, 190 parts; pale shellac, 95; rosin, 125; turpentine, 190; alcohol at 85 per cent., 1000 parts; by measure.
Varnish for Cabinet-Makers - Pale shellac, 750 parts; mastic, 64; alcohol, of 90 per cent., 1000 parts; by measure. The solution is made in the cold, wiuth the aid of frequent stirring. It is always muddy, and is employed without being filtered.
With the same resins and proff spirit a varnish is made for the bookbinders to do over their morocco lether.
For fixing engravings or lithographs upon wood, a varnish called mordant is used in France, which differs from others chiefly in containing more Venice turpentine, to make it sticky; it consists of - sandarch, 250 parts; mastic in tears, 64; rosin, 125; Venice turpentine, 250; alcohol, 1000 parts, by measure.
Copal varnish - Hard copal, 300 parts; drying linseed or nut oil, from 125 to 250 parts; oil of turpentine, 500; these three substances are to be put into three separate vessels; the copal is to be fused by a somewhat sudden application of heat; the drying oil is to be heated to a temperature a little under ebullition, and is to be added by small portions at a time to the melted copal. - When this combination is made, adn the heat a little abated, the spirits of turpentine, likewise previously jeated is to be introduced by degrees; some of the volatile oil will be dissipated at first; but more being added, the union will take place. Great care must be taken to prevent the turpentine vapor from catching fire, which might occasion serious accidents to the operator. When the varnish is made, and has cooled down to about the 130th degree of Fah., it may be strained through a filter, to separate the impurities and undissolved copal.
Almost all varnish-makers think it indispensable to combine the drying oil with the copal, before adding the oil of turpentine; but in this they are mistaken. Boiling oil of turpentine combines very readily with fused copal; and, in some cases, it would probably be preferable to commence the oparation with it, adding it in successive small quantities. Indeed, the whitest copal varnish can only be made in this way; for if the drying oil have been heated to nearly its boiling point, it becomes colored, and darkens the varnish.
This varnish improves in clearness by keeping. Its consistence may be varied by varying the proportions of the ingredients within moderate limits. Good varnish, applied in summer, should become so dry in 24 hours that the dust will not stick to it, nor receive an impression from the fingers. To render it sufficiently dry and hard for polishing, it must be subjected for several days to the heat of a stove.