Lacquer is so called because it usually contains gum lac, either shellac or seed lac. Seed lac is the original form of the gum or resin; after being purified it is moulded into thin sheets, like shell, and hence is called shellac. Shellac is frequently bleached so as to become quite white, in which state it forms a colorless solution. Bleached shellac is never as strong as the gum in its natural condition, and unless it be fresh it neither dissolves well in alcohol nor does it preserve any metal to which it may be applied.
There are many recipes for good lacquer, but the success of the operator depends quite as much upon skill as upon the particular recipe employed. The metal must be cleaned perfectly from grease and dirt, and in lacquering new work it is always best to lacquer as soon after polishing as possible. Old lacquer may be removed with a strong lye of potash or soda, after which the work should be well washed in water, dried in fine beech or boxwood sawdust and polished with whiting, applied with a soft brush. The condition of the work, as to cleanliness and polish, is perhaps the most important point in lacquering.
The metal should be heated and the lacquer applied evenly with a soft camel hair brush. A temperature of about that of boiling water will be found right.
A good pale lacquer consists of three parts of Cape aloes and one of turmeric to one of simple lac varnish. A full yellow contains four of turmeric and one of annatto to one of lac varnish. A gold lacquer, four of dragon's-blood and one of turmeric to one of lac varnish. A red, thirty-two parts of annatto and eight of dragon's-blood to one of lac varnish.
A great deal depends, also, upon the depth of color imparted to the lacquer, and as this may require to be varied, a very good plan is to make up a small stock bottle, holding, say, half a pint, according to any good recipe, and add as much of it to the varnish as may be required for the desired tint.
The following are a few favorite recipes:
Alcohol, 1/2 pint; dragon's-blood, 1 drachm; seed lac, 1 1/2 oz.; turmeric, 1/4 oz. Shake up well for a week, at intervals of, say, a couple of hours; then allow to settle, and decant the clear lacquer; and if at all dirty filter through a tuft of cotton wool. This lacquer may be diluted with a simple solution of shellac in alcohol and will then give a paler tint.
1. Turmeric, 1 oz.; saffron 1/4oz.; Spanish annatto, 1/4 oz.; alcohol, 1 pint. Digest at a gentle heat for several days; strain through coarse linen; put the tincture in a bottle and add 3 oz. good seed lac coarsely powdered. Let it stand for several clays, shaking occasionally. Allow to settle and use the clear liquid.
2. Take 1 oz. annatto and 8 oz. alcohol. Mix in a bottle by themselves. Also mix separately 1 oz. gamboge and 8 oz. alcohol. With these mixtures color seed lac varnish to suit yourself. If it be too red add gamboge; if too yellow add annatto; if the color be too deep, add spirit. In this manner you may color brass of any desired tint.
Best pale shellac (picked pieces), 8 oz.; sandarac, 2 oz.; turmeric, 8 oz.; annatto, 2 oz.; dragon's-blood, 1/4 oz.; alcohol, 1 gallon. Mix, shake frequently till the gums are dissolved and the color extracted from the coloring matters and then allow to settle.
4 oz. shellac and 1/4 oz. gamboge are dissolved by agitation, without heat, in 24 oz. pure pyro-acetic ether. The solution is allowed to stand until the gummy matters, not taken up by the spirit, subside. The clear liquor is then decanted, and when required for use is mixed with 8 times its quantity of alcohol. In this case the pyro-acetic ether is employed for dissolving the shellac in order to prevent any but the purely resinous portions being taken up, which is almost certain to occur with ordinary alcohol; but if the lacquer were made entirely with pyro-acetic ether, the latter would evaporate too rapidly to allow time for the lacquer to be equally applied.
Lacquers suffer a chemical change by heat and light, and must, therefore, be kept in a cool place and in dark vessels. The pans used should be either of glass or earthenware, and the brushes of camel's hair with no metal fittings.