By means of this, prints can be obtained more quickly than by any other process, but there is more trouble as the image is invisible till developed. The paper is coated with an emulsion the same as a dry plate, and is, therefore, equally as sensitive to light, and great care must be exercised to conduct all the operations in the dark room. When properly manipulated it yields prints of a fine engraving black colour without any gloss. The paper is placed in the printing frame with the sensitized surface next to the negative; some beginners find a difficulty in telling which is the sensitized surface, but there should be no such difficulty from the appearance, but if there is, the piece of paper should be laid on the palm of the hand for a moment when the sensitized surface will curl inwards. The back of printing frame being placed in position, the paper is then exposed to daylight for two or three seconds, or, preferably, to gaslight or lamplight, as more control is obtained over exposure; hold the frame about three feet off the gas-burner for 10, 20, or 30 seconds according to the density of negative, and for 30 or 40 seconds to lamplight. Experience alone can determine the duration of exposure. The paper is removed from the frame in the dark room, and placed in the developing dish, and water poured on it till the paper is thoroughly limp, the water being then poured off". The developer, Ferrous Oxalate. recommended on page 28, may be used; or the following is perhaps an improvement : -
Neutral Oxalate of Potash ... 1440 grains. Distilled Water......... 12 ounces.
Ferrous Sulphate......... 540 grains.
Sulphurous Acid ... ... ... 3 drops.
Distilled Water......... 4 ounces.
Add one part of No. 3 to seven parts of No. 1, and add Sulphurous Acid ... ... ... 1 drachm, and two or three drops of Bromide of Potash solution (page 26). Pour the developer evenly on the paper, and the image will soon begin to start into view. When the whole of the detail is visible, and the print is black enough, it is plunged immediately, without washing, into a clearing bath of
Acetic, Hydrochloric or Sulphuric Acid 1 drachm
Water ...................... 5 ounces, and allowed to remain for five minutes, and then into another bath of the same strength for the same time and then into a third. It should be then washed in water for 10 minutes, and fixed in a hypo bath of about four ounces to the pint, for about 15 minutes and then allowed to dry. Bromide Paper, as a rule, is sent out in three grades : - (a) smooth surface, thin paper, most suitable for mounting; (b) smooth surface, thick paper, for book illustrations, and (c) rough surface thick paper, most suitable for enlargements of portraits and portraits by contract printing described above.