If an article has been lacquered before, that lacquer must, in the first place, be removed, and the article afterwards carefully cleaned and polished. When the brass has not been lacquered before, it must receive before lacquering the highest possible finish and polish, if it is desired to make a fine job. This is done by taking out the marks of the file with finer and finer sorts of emery - paper or cloth, then polishing with rotten - stone or oil, and giving the article, after this has been cleaned off, a final touch with a buff - stick and crocus powder. The article must be carefully wiped clean, and care taken that it is not touched with the fingers after this has been done, as these would leave a greasy mark. Care must be taken at every step to invariably lay the successive strokes of the emery - cloth or paper and polishers in the same direction. When the desired degree of polish has been attained, a quantity of lacquer is poured into (say) an egg - cup, which is a very convenient receptacle for the purpose. A fine flat camel - hair brush is taken, and the article being gently warmed and held on the left hand, a small quantity of the lacquer is taken up on the brush, and the brush is drawn over the brass with straight strokes, always, if possible, in the same direction.

The article may generally be held by screwing a piece of wire into some hole in it, and holding the wire with a small hand - vice. As many coats of the lacquer as desired may be given by keeping the brass hot; the degree of heat is an important element in the success of the operation. Holtzapffel says it must not be warmer than boiling water; but so far as my experience goes, I should say the heat of boiling water would be too great. Considerable skill to required in lacquering well, and that skill can only be attained after a good deal of experience. The great secret of lacquering for beginners, at all events, is to take as little as possible of the lacquer at a time on the brush, have the article perfectly clean, a good brush with no loose hairs in it, and not make the article too hot.

Now as to lacquers. There are a great variety of them. As a rule, English brass - Work is covered with a very pale lacquer containing almost no colour; while, on the contrary, Continental lacquers contain too much colour. Wray's is a very fine specimen of lacquering. It has, however, in it a fugitive colouring material, and when a certain time elapses, the brightness leaves it. Zeiss's, again, has a great amount of colour in it. Wray's looks well when new; but it very soon fades, and the colour becomes bad. The simplest and best pale lacquer, Holtzapffel says, is made of shellac and spirits of wine only, in the proportions of about 1/2 lb. of the best pale shellac to 1 gal. of spirit. It is, he says, required to be as clear and bright as possible, and is always made without heat by continuous agitation for 5 or 6 hours. If not clear, it may be filtered, and should be kept out of the influence of light. It may be coloured for yellow tints with turmeric, Cape - aloes, saffron, or gamboge; and for red tints with annatto or dragons' - blood.

What I have described is the process adopted for lacquering the outside of photographic lens mounts, or all those portions of the brass - work where the light does not pass. The inside of the mounts, however, is treated in a totally different way. We must have, where light passes, a surface as nearly dead black as can be got. This is obtained, in the inside of the tubes, by mixing finely triturated lampblack with the lacquer used for the outside, and applying the black lacquer in one or more coats with heat to the inside of the tube. The result is a finely grained black surface which reflects no light. As soon as the surface has received one or two coats, no more must be given, as the repeated application of the lacquer would make the surface glossy - the very thing which it is wished to avoid. This method of blackening the brass does excellently for all portions which are not to come into contact with the fingers; but wherever the brass requires to be handled, we must have recourse to something different from lampblack. One of the modes adopted for that purpose is to bronze the articles. There are various - ways of doing this. Every one must be familiar with the ordinary greenish colour of gas - fittings which are bronzed.

The article is first thoroughly cleansed from all grease, and then dipped in vinegar or a strong solution of sal - ammoniac, or sal - ammoniac and vinegar mixed in the proportion of 1 to 3 oz. of the sal - ammoniac to 1 pint of vinegar. Holtzapffel says a quick bronze is made with 1 oz. corrosive sublimate dissolved in 1 pint vinegar. The best and most rapid, however, of all the bronzing liquids, is the nitro - muriate of platinum, called "chemical bronze.". It is known in the shops as the ter - chloride of platinum. This produces the colour very readily. All these methods, however, merely give a bronze tint, and not the black surface we should like to get. If I take a piece of clean brass, and touch it with the platinum solution, the bronze effect is almost instantly produced; but it does not, in my hands, produce black. The bronzing process is invariably used with all articles put together with soft solder. The method I am about to describe requiring a considerable amount of heat, the articles must be without any soldered joints.

When I first began to "work in brass" a great many years ago, at the lathe, I experienced much difficulty, sometimes not being able to give some parts of the articles I produced a sufficiently dead - black surface, such as the setting of lenses, lens - stops, and such. like.

Merely bronzing in such a case will not do, and lacquer and lampblack is worse. I became acquainted with an Edinburgh optician who had been taught his knowledge of brass - work finishing for philosophical instruments in the workshop of the late John Adie; he knew no method except bronzing. At that time he had a large business in the sale of the student's Nachet and Hart - nack microscopes, the brass stages of which are, perhaps, the most beautiful specimens of blackened brass which can be produced. We wrote to Nachet, and asked him how it was done, and, I think, he replied that it was done by nitrate of silver. We tried that, and failed. There was nothing for it but to fall back upon the bronze again. Some time after, when the Rev. J. B. Reade described his microscope kettle - drum condenser in the Proceedings of the Royal Microscopical Society, he incidentally mentioned that those portions of the mount which it was necessary to blacken - were blackened by nitrate of copper. My friend and I tried it almost as soon as I had read it, and we succeeded at once in producing a black surface which was everything we wished. I prepare the solution by dissolving copper wire in nitric acid, weakened by adding, say, 3 or 4 parts of water to 1 of acid.

The article to be blackened is heated pretty hot, and then dipped into the solution; it is then taken out, and heated over a Bunsen burner or spirit - lamp. When the article is heated to the proper temperature, the green colour of the copper first appears, and as the heat is increased, the article becomes of a fine dead black. It is not necessary to lacquer it. It seems better, to my thinking, to let it alone, just giving it a good brushing to remove the dust, and it may be considered finished. If, however, it gets a single coat of lacquer; the colour becomes blacker, and if there is not sufficient put on to make the surface glisten; - too much lacquer, however, invariably produces an objectionable polished surface. (W. Forgan.) See also Workshop Receipts, pp. 74 - 76.