If the plate is to be produced by the _swelled gelatine_ process, the negative is varnished and sent to the gelatine room. Here the gelatine is dissolved and the sensitized solution of bichromate of potash is added, and it is flowed on plate glass, then placed in a drying box, where a current of air is continually passed over it. When the gelatine is dry it is placed in a printing frame, in close contact with the negative, and exposed to the light. On removing the negative the picture is plainly seen on the gelatine, the action of the light having changed the color of the exposed portions of the gelatine, besides rendering those parts insoluble, while the parts protected from the action of the light, by the opacity of the negative, remain soluble, and are swelled up by immersion in cold water. The gelatine is then an exact opposite of the plate, the _whites_ being represented by the raised portions. From this mould, or relief, a cast is made in a preparation of wax or plaster, when it is ready for the stereotyper. For the _wash-out_ or photo-electrotype process, the negative, when dry, is not varnished, but is first coated with a rubber solution and then with plain collodion, after which it is immersed in a dish of acetic acid for about five minutes, when it is stripped from the glass and turned over. It is then what is termed a reversed negative. The method of preparing the gelatine is very much the same as for the _swelled_ process, with the exception that it is _cooked_ for about forty-eight hours, and with the addition of several preparations which are introduced at the time of sensitizing, to make it easily washed out. The negative is exposed in the same manner as described before, but the time of exposure is generally less. After being taken from the printing frame the gelatine is gently scrubbed with a line brush, and kept in tepid water until a very slight relief is obtained. It is then immersed in alcohol for a few seconds, and dried with a cloth, when it is covered with a preparation of lamp black and glycerine, which is allowed to remain about five minutes, when the surface of the plate is carefully rubbed with clean muslin, exposing the surface of the lines,—all this being done in a dark room before an orange light, which is non-actinic. The gelatine is now placed in a frame and exposed to the light from five to twenty minutes, the lampblack protecting the spaces between the lines from the action of the light, so that those portions remain soluble. The gelatine is again scrubbed until the proper relief is obtained, after which it is allowed to dry for about twelve hours, when it becomes hard and is ready to be electrotyped.