These are really a variety of slow bromide papers. They require a much longer exposure, but develop up much more quickly. Therefore, it is possible to handle them in very subdued artificial light in an ordinary room, and not necessarily in a dark-room - as a precaution the filling of the printing-frame and the developing should be done in the shadow of the body, or behind a sheet of yellow or canary-coloured paper.

The fixing-dish should be covered with a piece of cardboard. This renders the work safe and convenient.

The printing-board, Fig. 45, may be used for gaslight-paper printing, and if the easel be sufficiently large it will protect the paper, if the printing-frame is filled behind it.

The Exposure

This is carried out on exactly the same lines as bromide paper, and the necessary length of the exposure may be experimentally found in the same way, but instead of seconds the time may be one, two and three minutes at six inches from the flame. With any yellowness in the negative- - as sometimes met with where pyro has been the. developer - the exposure must be considerably increased. Incandescent gas is very useful for gaslight papers. Daylight may be used as a means for printing, but the exposure will be only a few seconds. A handy daylight-exposing arrangement can be made if the window-flap, B, Fig. 48, is weighted, so that it will work freely. The frame is filled in weak yellow light, and placed at a distance of eighteen inches or two feet from the opening. The exposure is made by opening and closing the flap. When the correct exposure is found, any quantity of exposures can be made before development is carried out.

Development

A useful developer may be made from the following formula: Metol, 1 grain; Hydroquinone, 3 grains; Sodium sulphite, 35 grains; Sodium carbonate, 35 grains; Potassium bromide, 1/2 grain; Water, 1 ounce. Dissolve in the order given.

Development is as for bromide papers; the image comes up at first in a somewhat streaky manner, but rapidly assumes its normal appearance, and unless it is critically watched it will be quickly overdone. The print should be removed just before it reaches its full strength, and allowed to finish in the fixing-bath. It should be rinsed in water previous to going into the fixer, and when in the latter it must be kept below the surface, otherwise it may become stained. It is advisable to cover the fixing-dish with a piece of cardboard. After fixing, the prints must be thoroughly washed and dried.

Toning Bromides

The normal colour of bromide papers is black and white. The matt surface paper gives an effect very similar to platinum paper. The colour of the sensitive surface may, however, be changed by toning.

Red

This is obtained by using the ordinary uranium intensifying bath, given on page 82.

Brown

The print may be converted to brown by immersing in a bath made of Hypo (ordinary fixing salt) and alum dissolved in boiling water. The bath is used hot, but not too hot.

Another method is to bleach the print in a bath of Potassium ferricyanide, 2 grains; Potassium iodide or bromide, 2 grains; Water, 1 ounce. It is then rinsed and placed in a bath of sodium sulphide, 5 grains to the ounce. Afterwards thoroughly washed.

Blue

A blue colour is imparted by immersing the print in a bath of Ammonio-citrate of iron, 5 grains; Acetic acid, 5 drops; Potassium ferricyanide, 3 grains; Water, 1 ounce.

Green

A bluish green may be obtained by treating the print first in the uranium ferricyanide bath for two or three minutes, until it is of a yellow-red colour, then transferring to the blue bath, in which, after some time, it will become green. The print should be washed in half a dozen changes of water, the superfluous moisture mopped off, and put to dry.