The plates we employed for pictures were copper faced with silver. The metal was hard rolled, and the plates, as received from the manufacturers, were flat and quite smooth, but not polished. The first step toward the preparation of the plate for use was to clip the corners and turn down the edges slightly, in a machine designed for the purpose, to bring the sharp edges of the plate out of reach of the buff employed in producing the necessary polish.

The plate was held, for scouring, in a block having clips on diagonally opposite corners for engaging the corners of the plate. One of the clips was made adjustable, to admit of readily changing the plates.

The scouring was effected by sprinkling on the plate the finest rottenstone from a bottle having a thin muslin cover over its mouth, and the rottenstone as well as the square of Canton flannel with which it was applied was moistened with dilute alcohol. The center of the Canton flannel square was then clasped between twow of the fingers, and moved round and round with a gyratory motion until the plate acquired a fine dead-smooth surface. The last traces of rottenstone were removed by means of a clean square of flannel. The plate was then transferred to a block mounted on a swinging support, and buffed by the vigorous application of a straight or curved hand buff formed of a board about four inches wide and thirty inches long, padded with four or five thickness of Canton flannel, and covered with buckskin charged with the finest rouge. Scrupulous cleanliness was imperative in every step of the process.

The plate, rendered sensitive to the light by the thin layer of bromo-iodide of sliver, was placed in a plate holder, and exposed in a camera according to the well known method. The time of exposure was much longer than that of modern photography. A great deal depended on the quality of the lenses of the camera. The exposure in the best cameras was reasonably short. The old time gallery, with its antiquated camera and fixtures, and the dark room with the appurtenances, are faithfully represented in the engraving.

After exposure, the plate was taken to another dark room for development. It was placed face downward over a flaring iron vessel, in the bottom of which there was a small quantity of pure mercury. The mercury was maintained at a temperature of 120 to 130 degrees Fah. by means of a small spirit lamp. The temperature was measured by a thermometer attached to the side of the vessel. The plate was raised occasionally and examined by the light of a taper, until the picture was fully brought out, when it was removed from the mercury bath and fixed.*

The fixing consisted merely in flowing over the plate repeatedly a solution of hyposulphite of soda, having sufficient strength to remove in about half a minute all the bromo-iodide of silver not acted upon by light. The plate was then thoroughly washed, and afterward gilded or toned by pouring upon it a weak solution of chloride of gold and heating it gently by means of a spirit lamp until a thin film of gold was deposited upon the plate and the picture attained the desired tone. The plate was then washed in clean water, and finally dried evenly and quickly over a spirit lamp.

This operation added to the strength and beauty of the picture, and also served to protect the surface of the plate to a great extent against the action of gases.

The finished picture was protected by a cover glass, and the edges of the glass and plate were securely sealed by a strip of paper attached by means of an adhesive coating.