OPTICAL INSTRUMENTS, PRESERVING.— All optical instruments, if required to be kept in good working order, should be carefully preserved from light and moisture, which have a peculiarly ruinous effect upon the glass. Lenses, when not required for use, should be kept in small chamois leather bags made to fit. If the brasswork of the lens become scratched and dirty, it may be carefully cleaned, polished, and relacquered. The lenses should be removed carefully, noting their position to avoid error in resetting, and the old lacquer removed with a rag dipped in methylated spirit. The brasswork is then polished with a piece of fine emery cloth, the rubbing of the cloth being done in one direction only. After sufficient polish has been obtained, a small quantity of a lacquer is poured into a saucer or egg-cup. This lacquer is composed of— Seed lac 12 ounces Copal 4 ounces Dragon's blood So grains Extract of red sanderswood so grains Saffron 70 grains Pounded glass pound Spirits of wine 2 quarts A fine flat camel-hair brush is the most suitable instrument for lacquering. The article is first warmed to a gentle heat, and the lacquer applied with the brush in one direction only, if possible. It will sometimes be convenient to hold the article by a piece of wire fitted into some
hole in it. It should not be heated to more than about 200 deg. Fahr. The principal points in lacquering are to keep the brush clean, and charged with as little of the solution as possible. The brasswork must also be quite clean, and not made too hot. Another lacquer, somewhat simpler to that already given, can be made by dissolving one half pound of the best pale shellac in one gallon of methylated spirit, and filtering. Yellow tints may be given to it by the addition of saffron or gamboge, or, if a redder color is required, annatto or dragon's blood should be added.
The inside of the lens mounts may be re-blackened by applying this lacquer in the same manner, the solution having been previously mixed with finely triturated lampblack. Only one or two coats should be given, or its surface will become glossy, and it is obvious that this is to be avoided.