The negatives for photo-etching are stripped and reversed in the same manner as for the _wash-out_ process. The metal generally employed for this process is zinc, though copper is sometimes used for very fine work. The zinc is very highly polished, and a thin sensitizing solution is flowed over it and dried, after which it is exposed under the negative to the action of the light. It is then rolled up with lithographic ink, placed in a dish of cold water, and gently rubbed with absorbent cotton, the ink readily leaving the unexposed parts, but remaining on the exposed lines or dots. It is then quickly dried and dusted over with dragon’s-blood powder, which adheres only to the remaining inked portions. The plate is then heated and cooled, and is ready for the etching bath, which consists of a small portion of nitric acid and water. After the first _bite_ the plate is again powdered, heated and cooled, and more acid added to the bath. This is repeated several times, after which the plate is ready for the press. The sides of the lines are protected by the manner in which the powder is applied after the first _bite_. The relief obtained in this way is greater than can be obtained by any other process. In reviewing the three processes above described, it is readily seen that the photo-etching process is the shorter method, no moulding or casting being necessary, and the sharpness of the finest lines is preserved in a manner impossible by the other methods. The plates are much deeper, and are equally suitable for the finest art work, down to the roughest newspaper work. This process, of which there are several modes of operating, has become very popular in the last few years, owing to the many improvements introduced by the _process inventors_, who have turned their attention to it. It has many advantages, among which is the fact that a plate can be put on the press within two hours from the time the copy is ready; and the wearing capacity of the plates is greater. By this process more than 300,000 impressions have been taken from plates of fine work, while swelled gelatine plates of the same character of work would not stand over 5000, and electrotypes 50,000 impressions. The main advantage of photo-etchings to the printer is, that the plates do not require constant washing up, as is the case with plates made by the other processes.