Lacquering is the application of transparent or coloured varnishes to metals, to prevent their becoming tarnished, or to give them a more agreeable colour. The basis of them is properly the lac described in the preceding article; but other varnishes made by solutions of other resins, and coloured yellow, also obtain the name of lacquer. Strictly speaking, lacquer is a solution of lac in alcohol, to which is added any colouring matter that may be required to produce the desired tint; but the recipes that have been published in various scientific journals contain apparently a great many useless articles. The following is much extolled, in Nicholsons Operative Mechanic, as a lacquer for philosophical instruments: -
3/4 oz. of gum guttae.
2 oz. of gum sandarac.
2 oz. of gum elemi.
1 oz. of dragon's blood, of the best quality.
1 oz. of seed lac.
¾ oz. of terra merita.
2 oz. of oriental saffron.
3 oz. of pounded glass; and 20 oz. of pure alcohol.
Before, however, the reader ventures to meddle with so formidable a list of ingredients as the foregoing, we would recommend him to make trial of the following more simple compound: - Take 8 oz. of spirits of wine, and 1 oz. of annatto, well bruised; mix these in a bottle by themselves: then take 1 oz. of gamboge, and mix it in like manner with the same quantity of spirits. Take seed-lac varnish, (described under the previous article Lac,) what quantity you please, and colour it to your mind with the above mixtures. If it be too yellow, add a little from the annatto bottle; if it be too red, add a little from the gamboge bottle; if the colour be too deep, add a little spirits of wine. In this manner you may colour brass of any desired tint: the articles to be lacquered may be gently heated over a charcoal fire, and then be either dipped into the lacquer, or the lacquer may be evenly spread over them with a brush.