Scientific American 4, 11.10.1851
Almost every workman that uses varnish has his own receipt for making it. These receipts are mostly remarkable for the number of ingredients, some of which are of scarcely any use, and others absolutely hurtful to the wished-for effect.
Brown rosin, gum sandarac, mastic, shell lac, seed lac, dissolved in strong spirit of wine, generally form the basis; Venice or common turpentine is added to prevent the varnish from cracking as it dried; camphor, anime, benzoin, alemi, are occasionally introduced; also gamboge, turmeric, dragon's blood, saffron, and lamp black as coloring ingredients.
The common varnish is made by dissolving 4 ounces of sandarac, and 6 ounces of Venice turpentine, in a pint of spirit of wine.
A harder varnish is made by dissolving 2 ounces of mastic, 1 ounce 1-2 of sandarac, and 1 ounce 1-2 of Venice turpentine in a pint of spirit of wine.
A very hard varnish, much used of late by the same of "French Polish for Furniture," is made by dissolving 3 ounced of shel lac, with 1 ounce each of mastic and shell lac in 2 pints 1-2 of spirit of wine in a gentle heat, making up the loss by ecaporation by adding more spirit at the end of the process.
The plain solution of either mastic or sandarac in the proportion of about three ounces to a pint of spirit of wine makes very good varnish.
Yellow varnishes are used by the name of lacquers to give a golden color to metals, wood, or leather: the following is, perhaps, that most used: color a pint of spirit of wine with three quarter of an ounce of turmeric, and fifteen grains of hay saffron; filter and dissolve in it two ounces each sandarac and elemi, one ounce each dragon's blood and seed lac, and three quarters of an ounce of gamboge.
Black varnish is made for sale by dissolving hald a pound of sandarac, and a quarter of a pound of yellow rosin, in half a gallon of spirit of wine, and then adding two ounces of lamp black to color it. But workmen generally make it by dissolving black sealing wax in spirit of wine.
The making of varnish from copal is a matter of difficulty, as copal is not soluble itself in its raw state in the spirit. One method is to add camphor to a pint of highly rectified spirit of wine until it ceases to be dissolved, and to pour this charged spirit upon dour ounces of copal, keeping up such a heat that bubbles may be counted. When cold pour off the varnish, and if all the copal be not dissolved, add more spirit impregnated with camphor. Another method is to heat the copal and let it drop as it melts into water; a kind of oil separates from it, and it becomes soluble in ardent spirit, and still more so if the melting is repeated.