Circular scratch-brushes, in which the wires are arranged radially, are used for scouring articles that admit of their use, such as table-ware and plated wares in general. These circular scratch-brushes are attached to the spindle of a lathe, and the wires consequently all receive a uniform motion in the same direction.

Scratch-brush Lathe.

The scratch-brush lathe shown in Fig. 22 consists of a circular brush of brass wires, with a metal or wooden

case, mounted upon a spindle running in two bearings, and driven either by foot or by steam power. The wires

are from 2 to 3 inches long, and the form of the brush is shown in Fig. 23. The top of the brush revolves towards the operator, who presents the object to be scratched, to the bottom.

The brush is surrounded by a wooden cage or screen, to prevent splashing. It is open in front, and above it is placed a reservoir of one of the liquids above named (generally, stale beer), from which a slender jet of the liquid is allowed to dribble upon the top of the brush. In order to protect the operator against the water projected by the rapid motion, there is fixed to the top of the frame a small inclined board, which reaches a little lower than the axis of the brush, without touching it. This board receives the projected liquid and lets it fall into a zinc trough which forms the bottom of the box. Through an outlet provided in one of the angles of the trough a gum tube conveys the waste liquid to a reservoir below.

Fig. 24 represents a lathe of different form, which is well adapted for pieces of small size. It is likewisę surrounded by a screen, to avoid splashing the operator and neighboring objects.

The above described hand and lathe scratch-brushes are made of wire of various gauges, from coarse to very fine, according to their intended uses.

When a hand scratch-brush becomes too short, the

twisted ends are cut off with a cold-chisel, and a new portion of wire is uncovered by removing part of the string wrapping. The best way to remove the twisted wire ends

is by resting the scratch-brush upon a lead block, and cutting them off with a sharp cold-chisel, if possible with one stroke of the hammer. This operation is represented in Fig. 25.

Scratch-brushes must be carefully looked after and their wires kept in good order.

When they begin to curl, they are now and then beaten with a mallet of boxwood, upon a small block held between the knees, so as not to produce a dead stroke.

Fig. 25.

Scratch-brushes kept too long in water become hard. If they become greasy, they are cleansed in caustic potassa; when oxidized, they must be cleansed in the mixed acid bath. This last operation, and even the dipping in aqua fortis, are sometimes resorted to for diminishing the size of the wires, and to soften the brush.

The lathe-brush is now and then turned over, face for face, in order to change the direction of the wires.

A few practical men have tried, by means of suitable devices, to run the lathe-brush constantly immersed in the liquid. But the resistance offered by the liquid requires so much more power to drive it that the method has been abandoned. If it were practicable this method of running the lathe-brush would be very desirable both on the score of cleanliness and because it would afford a more complete

protection against the oxidation of the wires by the acid fumes of the workshop.

Scratch-brushing is an important operation, the more so that many articles are delivered to the trade without any further manipulation. It is therefore advisable for beginners to become thoroughly practised in it before they venture to experiment upon articles of considerable value.

Another apparatus employed for scratch-brushing and polishing consists of a quantity of disks of muslin held together by side washers and nuts, and mounted upon a mandrel or arbor revolving with great velocity. These buffing wheels, as they are called, are flexible, and follow the irregularities of shape of certain articles. They receive now and then a small quantity of rouge or pumice-stone, or any other suitable polishing or abrading material.

CHAPTER V.

CLEANING BY ATTRITION (TUMBLING),

VERY small articles, that cannot be scratch-brushed, are cleaned by attrition, either dry or wet. For this purpose the articles are placed in a long and narrow sack, to which a regular to-and-fro motion is given, thus occasioning a constant friction by the rolling of the articles over each other. In some cases, as where, for example, it is desired to lighten the gilding of pearls, diluted vinegar is used in the operation. In other cases sawdust from fir or box-wood is employed for drying the small articles, and at the same time increasing their brightness.

The operation is sometimes performed by hand. The articles to be brightened are introduced, together with