A Manual Of Photography

48 HISTORY OF PHOTOGRAPHY. be only dried, and not polished. This includes the first preparation of the plate, which may he made a long time pre- viously. “Second Preparation.—I do not think it fit to allow a longer interval than twelve hours to intervene between this operation and iodising the plate. We left the plate with a deposit of gold and platinum. In order to polish this metallic layer, the plate is rubbed with a piece of cotton, and oil and rouge, until it again becomes black ; and then with alcohol and cotton only, in order to remove this layer of rouge as much as possible. The plate is again rubbed very strongly, and passing several times over the sanie places, with cotton impregnated with cyanide. As this layer dries very promptly, it might leave on the plate traces of inequality : in order to avoid this, the cyanide must be again passed over it, and, while the plate is still moist, we quickly rub over the whole surface of the plate with cotton imbibed with a little oil, thus mixing these two substances; then, with a piece of dry cotton, we rub, in order to unite, and, at the same, to dry the plate, taking care to remove from the cotton the parts which are moistened with cyanide and oil. Finally, as the cotton still leaves traces, the plate is likewise sprinkled with a little rouge, which is removed by gently rubbing. “ Afterwards, the plate is again rubbed with cotton impreg- nated with oil, only in such a manner as to make the burnish of the metal return ; it is then sprinkled witli rouge, and then very gently rubbed round, to remove all the rouge, which carries with it the superabundance of the acidulated layer.1 Finally, it is strongly rubbed with a rather firm pledget of cotton, in order to give the last polish." " It is not necessary often to renew the pledgets of cotton imbibed with oil and rouge ; they must only be kept free from dust. I have said above that the first preparation of the plate may serve indefinitely ; but it will be comprehended that the second must be modified, according to whether we operate on a plate which has received a fixed or an unfixed impression. 1 This must be done as gently as possible ; for otherwise the rouge would adliere to the plate, and would form a general film. 2 In operating on a plate a long time after it has received the first prepa- ration, it is necessary, before employing the acidulated oil and red oxide, to manipulate, as 1 indicate further on, for the plate which has received a fixed impression. This precaution is necessary lor destroying the stains which time may have developed.