BRASS is finished by different classes of artizans, by methods that are widely dissimilar, many of which are described; and it may be considered that the same modes are also suited to the other alloys, consisting principally of copper, such as gun metal, electrum, or German silver, etc, particularly as regards parts of machinery and mathematical instruments. 1. - Turned Works in Brass are frequently polished with emery paper alone, two sizes of which are mostly used with a little oil. For plane and cylindrical surfaces, the emery paper is wrapped around a parallel piece of stick, and for internal plane surfaces it is applied by means of a small cubical block of wood; these methods tend to preserve the external angles from being rounded. An additional lustre is given, if required, by woollen cloths with oil and rottenstone. When the work is not to be varnished, a minute quantity of the polishing oil is left on, which somewhat prevents tarnishing.
The sliding tubes of telescopes, after having been cleaned off with fine emery paper, are brushed with a revolving or wheel brush, with fine crocus and oil, and are finished with a woollen rag and rottenstone, nearly free from oil, and rubbed lengthways, the lathe being for the time at rest.
2. - Common Flat Works, after they have been filed up, are frequently finished first with coarse and then with fine emery paper, which is often used dry or without oil, and wrapped around a file or wooden rubber. The grain is usually laid straight, or in one direction; at other times the works are coarsely curled by a circulating motion of the hand.
3. - Superior Flat Works. - The brass plates for the mechanism of harps are perhaps more carefully treated than any of this kind. The plates of the harp machinery are planed and scraped, the mechanism is then fitted, and the second axes or arbors are ground into their respective pivot-holes with fine oilstone powder. The plates are again carefully scraped, after which they are polished, 1st, with" charcoal in the stick, to remove all the marks made with the scraper and file. 2ndly, flour emery is dusted over the plate from a muslin bag, and rubbed with a piece of wood three or four inches square, covered with baize nailed around the edges, to serve as a rubber. 3rdly, rottenstone is similarly employed upon a rubber covered with two or three thicknesses of fine woollen cloth; the plate is then washed quite clean and dried. 4thly, it is finished with a dry buff rubber and rottenstone; the holes are then cleaned out with a feather slightly coated with dry whiting, and finally the plate is varnished. In all the processes it is necessary to follow the curvature of the plate, in order to lay the grain in accordance therewith.
Brass door-plates of the best kind are treated with nearly the same care, although immaterial variations are often made in the routine.
4. - Flat Works in Mathematical Instruments. - Such of these as are in brass and gun metal, when left from a very smooth file are prepared first with a stick of water of ayr stone; and are afterwards finished with water of ayr stone scraped to a fine powder, mixed with a little oil to the consistence of treacle, and applied with a smooth piece of white deal. If the work present lines from the grain of the wood, it is rubbed with the clean finger, or a buff stick smeared with oil, the polishing stuff that remains on the work being sufficient for the concluding step.
The edges of work, after having been drawfiled, are scraped with a sharp triangular scraper, applied almost without pressure, in order to avoid utters or indentations; oilstone powder with oil is next used on a piece of mahogany, then scraped water of ayr stone, as above, and lastly, a buff stick with dry rottenstone.
5. - Flat Works Curled. - These are filed, scraped, and stoned, as by the mathematical instrument makers. The work is then clouded with a piece of charcoal and water, by means of which the entire surface is covered with large curly marks, which form the ground. The curls resemble an irregular cycloidal pattern, with loops of from one quarter to one inch diameter, according to the magnitude of the work. Similar, but much smaller marks are then made with a piece of snake-stone, blue-stone, or even common slate pencil, filed to a blunt point. The general effect of the work much depends upon the entire surface being uniformly covered, with which view the curls should be first regularly continued around the margin, the central parts are then filled in; after which the work is ready to be varnished.
The curled surfaces are desirable, in so much as any little accidental injuries or rubbing, arising from the continued use of the articles, are less observable upon curled surfaces than upon similar pieces laid with an even grain; and the curled parts mixed with the bright edges have a good effect. The mode was introduced by the author's father.
6. - Watchwork in Brass. - Flat works of medium character, after having been filed, are polished, 1st, with a stick of blue stone and water, and 2ndly, with a slip of box wood, with the unguent obtained by rubbing two pieces of blue-stone together with oil. The best and flattest watch works, after 1st, the blue-stone, are polished 2ndly with pewter and red stuff or crocus, and 3rdly with a piece of tortoiseshell, horn, or ivory, supplied with very fine red stuff and oil.
Tortoiseshell is preferred for the polisher, as it may be used nearly dry and leaves the fewest streaks or shades in the work; horn is next in estimation, and ivory the least of the three; each of which materials, and also pewter, glass, etc, are used in flat pieces from one to two inches square, which are smeared with the powders mixed with oil; the work is then rubbed on the surface with the fingers, as if it were the muller used in grinding paint; this produces very flat surfaces. The burnisher is sometimes used after the powders.
Most of the brass work of watches is gilt by water gilding, to prevent it tarnishing from the effect of the atmosphere. The polishing of the steel part of watchwork is described under the head Machinery in iron and steel in this catalogue, article 13.
7. - Braziers Works. - The coppersmiths and braziers adopt nearly the same treatment for brass as for copper. Subsequently to the brass work having been annealed for the last time, and before it is planished with the hammer, it is generally pickled with nitrous acid diluted with very little water, and then scoured with coarse red tripoli and water to remove the oxidation caused by the fire. The work when planished is cleaned 1st with crocus and oil; 2ndly, the oil is rubbed off with whiting; and 3rdly, the final polish is given with dry rottenstone usually applied on an old worsted stocking.
8. - Stamped Works in Brass, for house furniture, such as finger plates for doors, and numerous other objects stamped out of sheet brass, are treated in a manner entirely different from all the preceding, as the sheet brass when carefully rolled is left very smooth and only requires to be made bright. The stamped works are 1st cut out, 2ndly figured between dies, in a fly press, or under a stamp hammer usually called a force, 3rdly they are annealed, 4thly coloured by immersion in an acid preparation, 5thly washed and dried in sawdust. The entire surface is now of a rich yellow or gold colour but dead or dull, 6thly the parts desired to be bright are burnished with a steel burnisher which is lubricated with water alone, or with water having a trifling admixture of vinegar or beer, and 7thly the work is varnished. The methods of colouring, bronzing, and varnishing, stamped works and others of the same character, will be hereafter detailed. 9. - Cast Works in Brass for House Furniture, including lamp and gas fittings. These works receive little or no polishing by the ordinary methods of abrasion with powders, which would be too tedious and expensive a process. The smallest and commonest of the castings, after having been cleaned by the brass founder, in the rumble, are coarsely filed and then scraped; those pieces which are more carefully moulded, as described under fine casting, (vol. i. p. 341,) require only the removal of the rough edges or burrs, and the tubes employed in gas works, etc, are left sufficiently smooth from the draw-plate. The several parts after having been adapted together, by aid of the file, turning tool, screws or solder, are almost exclusively decorated by the processes of dipping, bronzing, burnishing and varnishing; part of which processes, as noticed in the last article, will be treated of towards the end of this volume.