the apparatus. The best substances for the pupose are sand and emery paper, or, preferably, a rag with finely powdered pumice-stone or ashes.

The apparatus should, in all cases, be handled gently, as any rough usage will be apt to endanger the sharpness of the knife-edges; and, lastly, the apparatus should not be called on to carry a greater weight than that for which it is intended.

CHAPTER XXXIX.

BURNISHING.

BURNISHING is the operation by which the asperities or surface irregularities of an object are flattened down by friction, with an instrument called the burnisher, so that all the molecules of the surface are, as far as practicable, levelled to the same plane which then reflects the light as does a well-polished mirror.

Burnishing is therefore an important operation for improving the appearance of electro-deposits, which are constituted by the juxtaposition of a multitude of small crystals with vacant spaces between them, and with facets reflecting the light in every direction. There is, moreover, a great advantage in flattening down these crystals, as by so doing we close the meshes of the network presented by all deposits obtained by the humid way. The deposited metal is at the same time hardened, and, so to speak, forced to penetrate into the pores of the underlying metal. The durability of the coating is thus increased to such an extent, that there is no exaggeration in affirming that, with the same amount of silver, a burnished article will last twice as long as one which has not been so treated.

The instruments employed for burnishing are made of various materials, but all of them must fulfil the requisite conditions of great hardness and a perfect polish.

Hardened cast-steel and several varieties of quartz such as agate, flint, and blood-stone, answer the purpose. For burnishing metallic electro-deposits, steel and blood-stones are especially used. There are several qualities of bloodstone. It should be hard, and must have a close texture without seams or veins; it should leave no white lines on the burnished parts, nor take off any metal, and its color should be of an intense black-red. Burnishers of steel

must have a fine, close grain, and be susceptible of taking perfect polish. Should the polish of any of the burnishing tools become impaired by use, it is restored by friction upon a pad of skin or leather attached to a wooden block, which is fixed to the bench by four protruding points of iron (Fig. 128). The pad is charged with polishing rouge

Fig. 128.

(colcothar, sesquioxide of iron), in impalpable powder, or, preferably, with pure alumina obtained by the calcination of ammonia alum. Venetian tripoli; rotten-stone, puttypowder, emery, and many other hard substances in a state of fine division, may also be employed.

The shapes given to burnishing tools are various (Fig. 129). Some are lance-shaped, others resemble a tooth, or a knife; others imitate a hind's foot, the olive, a half sphere, a dog's tongue, etc. etc. A considerable stock of these instruments is necessary.

The burnishing operation is divided into two distinct parts: the first consists in roughing, and the second in

finishing. The tools are also of two kinds: the first presents quite a sharp edge, whereas the latter has a rounded

Fig. 129.

surface. An experienced worker cannot be induced to part with a good burnishing tool, since he is so fully cognizant of its value for rapid and successful work.

The operation is conducted in three different modes: by hand, on the lathe, and by the arm. The tools for the hand or the lathe are fixed, by means of copper ferrules. to wooden handles, cylindrical and short, in order that the hand be not influenced by their weight. On the con trary, the tools for the arm or the vise are fastened to wooden handles sufficiently long to rest their slender part upon the arm or the shoulder, whereas the stouter por tion is grasped by the hand.

The burnisher's tool and the objects are frequently moistened with certain solutions, some of which simply facilitate the sliding of the instrument, while the others have a chemical action which affects the shade of the burnished articles. The first category comprises pure water, solutions of soap, decoctions of linseed, and infu

sions of the roots of marshmallow or liquorice; the second includes wine-lees, cream of tartar, vinegar, alum-water,

etc.

To burnish the gold applied upon electro-deposits of copper (as is the case in dead gilding by that method), it should simply be wet with saliva, for fear of producing a disagreeable red shade. A solution of dark soap is generally preferred by operators, although when old it imparts an unpleasant tinge, due to the decomposition of sulphur compounds, that it often contains.

In some establishments, in which plated table-ware in large quantity is turned out, ingeniously devised burnishing machines driven by power are in use, by which much of the manual labor is spared. Without an illustration it would be useless to attempt a description of these machines. The knife, spoon, etc., each supported by its tips in a suitable holder, are slowly rotated, while the burnishing tool moves quickly over the surface, performing the work rapidly and satisfactorily.

When the burnishing is completed, the surface is wiped off longitudinally with an old, soft, calico rag; sawdust, hard cloth, and tissue paper produce streaks.

The finish obtained by burnishing is satisfactory when it reflects the luminious rays like a mirror. Should the presence of mercury, or a bad deposit, or any other cause prevent the tool from producing a bright surface, the object is said to be greasy.

Articles which have been previously polished, such as steel mountings of lady's hand bags, and the like, and which generally receive a mere film of electro-deposit, are not burnished, but simply rubbed with a chamois skin and rouge of the finest quality.

On the other hand, electro-deposits that are too thick, or that have been laid too rapidly, cannot be burnished,

but are polished on the buffing-wheel-a wheel made of a large number of circular disks of cloth, held firmly together by flanges of wood, and mounted on a spindleor by rubbing with a skin impregnated with a mixture of oil and some hard powder, like pumice-stone, tripoli, putty-powder, rouge, etc. Coarse powders are used at the beginning, and finer ones at the end of the operation.

There is, therefore, a great difference between polishing and burnishing, since the former levels the surface by removing the asperities, whereas the latter crushes and flattens them.

Polished silver deposits are more agreeable to the eye than burnished ones; but the hardening of the latter renders them more durable.

CHAPTER XL.

STOPPING-OFF" VARNISHES.

"STOPPING-OFF" is the manipulation by which certain parts of a metallic article (which may be already covered with an electro-deposit on its whole surface) are coated with another metal. For instance, if it be desired to gild the parts in relief of an object, the body of which is silvered, the other portions are "stopped-off," and vice versa. This operation is easily performed, and simply requires a little practice and care, and especially a firm hand to make thin lines with the hair pencil.

The method of procedure is as follows:

After having thoroughly scratch-brushed and wiped off the object, the parts which are intended to remain with the primitive color are covered by means of a brush with