The reflector-plate consists of virgin-silver and the purest copper (from the ingot), in the proportion of 6 oz. of silver to 16 oz. of copper. The two metals are in pieces, forming a flat parallelopepid of about nine inches of surface. Being first thoroughly scraped and cleared from rust with a file, they are tied together with wire and placed in the furnace, where they are united by means of a flux composed of burnt borax and nitre, mixed to the consistence of cream. Their thickness is sufficient to admit of their being repeatedly passed through the rolling-mill, so as at last to come out a plate twenty-eight inches square. Every time it is passed through the rollers, the plate is annealed in the furnace before being again pressed. It is then cut into a circular disc ready for working; and great care should be taken to keep the metal perfectly clean during the whole of the hammering and polishing processes. The first step towards forming the plate to the curve, is to raise the back or copper side to a slight convexity by beating, with the boxwood mallet (fig. 99), rounded at each end, c and d, its inner or silver side upon a large block of beechwood, of a form slightly concave. This beating is begun at the edge of the plate, and gradually reaches the centre. After the disc has been raised to the proper height on the wooden block, the next step is to take it to the horse (fig. 103, opposite page), where it is beaten with the wooden mallet (fig. 100), its concave face being in contact with the bright steel-head a (fig. 103), until it has nearly reached the proper height for the reflector, for which the workman has a gauge or mould to guide him; in this course of raising, as it is called, the peened face b a b (fig. 100) is first used, and then recourse is had to the opposite or flat face for smoothing it after being raised. In this last course of raising, as well as in the process of smoothing the reflector all over, the workman bestrides the horse.

During the process of raising with the peened side of the mallet, an external mould FGHF (fig. 101), with a needle-point P, at its vertex, is applied, to indicate its proper position with reference to the mould; and allowance is made on the height and diameter of the reflector to meet the expansion of the metal during the hard-hammering which is to follow. After each course of the raising with the wooden mallets, the reflector must be annealed in the following manner:—The reflector is first damped with clean water, and its surface dusted over with a powder, composed of one pint of powdered charcoal to one ounce of saltpetre, which is applied by means of a thin flannel bag. The reflector is then put on a clear charcoal fire, where it is turned round as the powder flies off, which is an indication that the metal is duly heated. Over-heating is very injurious. When removed from the fire, the reflector is plunged into a large tub, containing what is called the pickle, which is a solution of one quart of vitriol in five or six gallons of water. After this it is washed with clean water, and scoured with Calais sand.

The next step is to put the reflector, thus raised nearly to its true form, into an iron stool, where a small hole being drilled in its vertex, a circle is described from this point with a beam-compass, so as to cut the paraboloïd to the proposed size.

The reflector is next hard-hammered all over (or planished, as it is technically termed) on the bright steel-head a (fig. 103), with the planishing hammer (fig. 102); and to facilitate working, the reflector is slung in a flexible frame SS, and counterbalanced by a weight w, hanging by a cord over the pulleys p p. When the reflector is all planished over, the next process is the smoothing, which is done on the steel-head a, with a lighter hammer (fig. 104 ), muffled with fine parchment at each end. After it is smoothed comes the finishing, or what is called the filling up to the mould. This is a tedious process, and the workman requires continually to have recourse to the marble table at M, on which he lays the reflector, as shewn in fig. 105, and applies to successive portions of its surface the mould g n, which has a needle-point centred at n, in the small hole drilled in the vertex. During this examination, he marks with a fine slate-pencil those portions of the reflector which do not meet the mould g n. The parts, so marked, are gently gone over with the muffled hammer, until every point touches the mould. This last process requires great caution; for, if any part of the surface be raised above the gauge, it is hardly possible to remedy it. Such a mistake, indeed, can only be corrected by annealing the reflector afresh, and bringing it back to the true form with the mallet; but reflectors so cobbled are never good. The table M (fig. 105) rests on a square box C, in which the tools and moulds are kept.

When thus finished from the hammer, the reflector is put into the apparatus shewn in fig. 106, which is placed at the end of a long dark corridor. RR is a wooden frame fixed to the wall with projecting brackets at K, which carry the reflector, fixed at E, E, by means of screws, so as always to have a definite position with reference to the bracket B, which carries the lamp and its fountain f, so arranged that its flame may admit of perfect adjustment to the point which ought to be the focus of the reflector. For the purpose of this adjustment, S shews screws for raising and depressing the level of the burner; and the lines or marks M, M′ shewn at the sockets J being brought into line, regulate the position of the burner in the plane of the focus, after it has been raised to the level of that plane by means of the screws at S. The lamp being lighted and thus properly placed, its effect on the reflector’s surface is observed by some one stationed at a convenient distance; and if the whole surface appear luminous, the instrument is considered fit for polishing; but if any dark spaces be found in it, the whole reflector must be again carefully tested by means of the mould, and the defective parts remedied in the manner above described.

The next step is to turn over the edge of the reflector, so as to stiffen it. For this purpose it is placed in the matrix P′P′ (fig. 107), and the needle-point at V is adjusted by the screw at D, so as just to enter the small hole formerly drilled in the vertex of the reflector. The die-plate PP (which is worked by means of the arms AA, which turn the screw S) then descends and presses the edge over, which is finished with a finely polished tool C, revolving round the axis of the instrument, which coincides with the centre of the matrix and die. In order to ensure a steady vertical movement of the die-plate PP, cross-arms FF, which are provided with sockets HH, which slide over the rods GG, GG, are added to prevent any lateral shake or derangement. The whole frame is stiffened by the cross-head in which the screw S works.

The reflector is then placed on the circular cast-iron table (figs. 108, 109), to which it is attached by the clamp-screws S, S. In this position, the bizzle W (fig. 108) and back-belt NAN (fig. 109), are soldered on. After this the reflector is ready for being finally polished; for which purpose, it is placed in a chaise percée, padded round the edges, and is first scoured all over with a piece of pure charcoal of hard wood, and next with a mixture of Florence oil and finely washed rottenstone, applied by means of a large ball of superfine cloth. It is then carefully cleansed with a piece of fine flannel dipped in Florence oil, and afterwards dusted over with the powder of well washed whiting, and wiped out with a soft cotton cloth. Lastly, it is carefully rubbed by the naked hand, with finely washed rouge and clean water, and wiped with a smooth chamois skin. In all the polishing and cleansing processes, some skill in manipulation is required, as the hand is generally moved in such a manner as to describe successive circles with their planes parallel to the lips of the reflector, and their centres in the axis of the generating curve.

The prices paid to the workmen for the various departments of the reflector-making are generally as follows:—

The prices paid to the manufacturer were for the large reflectors of 24 inches aperture, L.43; for the small ones of 21 inches, L.31, 12s. The lamp with the sliding-carriage, required for each, costs L.6.