Shellac Varnish & Finish
The properties of orange shellac varnish and shellac finish.
¶ Shellac is not an exudation of tree gum as are many of the other resins used for varnish making, although it is collected from trees. It is a resinous incrustation found on certain species of trees in the jungles of India, Siam, Ceylon and other far Eastern countries. It is deposited on the bark, branches and twigs of these trees by swarms of tiny insects known as the Lac insect (coccus Lacca). These twigs are broken off and in that form are called stick lac. They are collected in June and September of each year by the natives and are crushed and ground in primitive stone mills to separate the gum from the wood. Then it is sifted to free it from bark., twigs, etc. Next it is placed in large tubs of warm water to free it from lac dye coloring matter which the insects have deposited. In this form it is known as seedlac.
¶ When the seedlac is dry it is placed in cotton bags and held over charcoal fire by two men, one at each end, who twist the bag when, the seedlac melts, thus forcing the melted gum through the weave of the cloth from where it is scraped and spread in a thin sheet over the outside of a hollow cylinder filled with hot water, or on flat surfaces. When the gum has congealed on this cylinder surface it is scraped off and broken into flakes with a knife and forms the dry shellac which comes to the finisher and painter.
¶ The natural color of shellac is bright orange. White shellac is prepared by bleaching orange shellac by a chemical process. The best grades of shellac are those which are most nearly free from impurities. Since most impurities are dark in color it follows that the lighter colored shellacs are apt to be the best.
¶ The dry guin shellac is soluble in alcohol (wood, denatured or grain) and in alkali water solutions, but not in turpentine, oil or benzine. Denatured alcohol is most commonly used for making shellac varnish by dissolving shellac gum in it. Wood alcohol is more expensive, usually, and is very poisonous. The fumes from it are injurious to the finisher's health and it is more difficult to brush shellac mixed with wood alcohol than that mixed with denatured alcohol.
¶ Pure grain alcohol is considered better than denatured or wood for cutting shellac gum, but that is not to be had in the United States, except under license. The best denatured alcohol for cutting shellac is the U. S. Government Formula No. 1. It calls for the use of 190 proof grain alcohol denatured by adding 5 gallons of wood alcohol (poison) to 100 gallons of grain alcohol. It is practically as good as pure grain alcohol for this purpose. Manufacturers using it are kept under bond to prevent the sale of this denatured alcohol unless mixed with at least 2 pounds of shellac gum per gallon. The denatured alcohol sold on the open market to painters contains more wood alcohol or other poison. For this reason a little better shellac can be purchased in the liquid form from manufacturers than the painter can mix by cutting shellac gum with the denatured alcohol which he can get, but on the other hand what he can mix is good enough for many purposes if he thinks it is wise to spend the time required to do the mixing.
Next Page: Shellac Mixing, How to Make Shellac.
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