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Laquers and Spirit Varnishes
Lacquers
- The term" Lacquer" is rather loosely used in the trade.It is generally applied to spirit varnishes, made from shellac, dammar, mastic, sandarac, or a similar resin, dissolved in a suitable solvent.
Coloured lacquers are prepared by adding a certain amount of colouring matter in the form of a dye, so that the solution is transparent.
Following American practice, the name" lacquer" is sometimes used to denote cellulose or syntheticresin varnishes.
It may, on occasion, also refer to oriental lacquer, a product quite different from other resinous materials.
Oriental lacquer, which is derived from trees which flourish in China and the Far East, is the basis of the well-known oriental lacquer ware and, except in this form, is seldom imported into this country.
Spirit Varnishes
The most important resin which is employed in the making of spirit varnishes is shellac, though sandarac, mastic, copal, amber, and others are frequently used.The process of manufacture, as usually carried out in this country, is comparatively simple.
The gums and solvents are placed in a wooden barrel which is made to revolve horizontally until complete solution takes place.
Methylated spirit is generally employed as a solvent.
French Polish.- This is a clear varnish for use on wood where only a very thin coat is required.
There are many recipes for its manufacture, but a good-quality polish can be made by dissolving 1 lb. of orange shellac in 1 gal. of methylated spirit, then adding 2 oz. of gum sandarac and 2 oz. of gum benzoiir.
Before applying, the wood is " filled" by rubbing on a mixture of plaster of Paris and tallow.
Then the polish is put on by rubbing with a soft cloth dipped in methylated spirit.
The rubbing should be in a circular direction, light, then hard.
A finishing-off coat is given consisting of the above polish diluted by adding methylated spirit.
Knotting.- The purpose of knotting is to protect paint against knots and other resinous exudations in wood, and, except in very bad cases, it is usually effective in doing so, provided that it is of good quality.
In theory, it consists of a solution of pure shellac in pure methylated spirit, the proportions being from 2 to 2½ lb. shellac to each gallon of spirit.
In practice, however, the shellac portion is often partly or entirely replaced by a less-expensive substitute; even rosin is occasionally employed for this purpose, thereby increasing the trouble which the application of the knotting is intended to prevent.
When purchasing shellac knotting, therefore, decorators should stipulate that it is guaranteed pure and free from rosin.
Associated Pages: xxxxx VarnishessxxxxxxResinsxxxxxxGumsxxxxxxGold Size