NITRIC ACID, ROUGE, DRY IODINE, MERCURY, DRYING POWDER, HYPOSULPHITE OF SODA, CYANIDE OF POTASSIUM, CHLORIDE OF GOLD; OR ROTTENSTONE, HYPOSULPHITE OF GOLD. TRIPOLI, CHLORIDE OF SILVER. CHLORIDE OF IODINE, } their compounds, or other BROMINE } accelerating mixtures. FIRST OPERATION.--Cleaning and polishing the plate.--For this purpose the operator will require the-- Plate Blocks, Plate Vice Spirit Lamp, Polishing Buffs, Nitric Acid, diluted in fifteen times its bulk of water Galvanic Battery, to galvanize the plate, if it is too imperfect to be used without, previous cleaning it, as directed in the last chapter. Rottenstone, Tripoli, which is too often dispensed with. Rouge, or lampblack--the first being most preferable. The English operators mix the two together. Prepared cotton Wool, or Canton flannel. If the first is used, it should be excluded from the dust, as it is not so easily cleansed as the latter. The plate is secured, with its silver side upward, to the block, by the means described on page 58--having previously turned the edges backward all around. The amount of cleaning a plate requires, depends upon the state it is in. We will suppose one in the worst condition; dirty, scratched, and full of mercury spots, all of which imperfections are more or less to be encountered. The mercury spots are to be removed by burning the plate. To do this hold the plate over the flame of a spirit lamp, more particularly under the mercury spots, until they, assume a dull appearance, when the lamp is to be removed, and the plate allowed to cool, after which it is attached to the block. Place the block upon the swivle, and hold it firmly with the left hand; take a small knot or pellet of cotton, or, if you like it better, a small piece of canton flannel--wet it with a little diluted nitric acid; then sift some finely prepared rottenstone--Davie's,* if you can get it--upon it, and rub it over the plate with a continual circular motion, till all traces of the dirt and scratches are removed; then wipe off the rottenstone with a clean piece of cotton, adopting, as before, a slight circular motion, at the same time wiping the edges of the plate. Even the back should not be neglected, but throughly cleansed from any dirt or greasy film it may have received from handling. * Sold by E. Anthony.