A Manual Of Photography

M. MARTIN’S CALOTYPE PROCESS. 229 the sheet is equally spread ; repeat this operation several times until the air-bubbles disappear ; taire also the precaution to keep the upper side of the paper dry. In order to prevent the fingers from spotting the paper, pass a bone paper knife under the corner of the sheet, to lift it from the slab between that and the thumb. Let the sheet remain upon the slab until the formation of the chloro-bromo-iodide of silver is perfect. This may be known by the disappearance of the violet colour which the back of the paper at first presented ; it must not be left longer, otherwise it would lose its sensitiveness. The time required to effect this chemical change is from one to five minutes, depending upon the quality of the paper. Spread upon a glass, fitted to the frame of the camera, a piece of white paper well soaked in water ; upon this place the pre- pared sheet, the sensitive side upwards. The paper which you place underneath must be free from spots of iron and other impurities. It is also necessary to mark the side of tire glass which ought to be at the bottom of the camera, and to keep it always in- clined in that direction when the papers are applied ; if this precaution is neglected, the liquid collected at the bottom, in falling over the prepared paper, would not fail to produce spots. The paper thus applied to the glass will remain there for an hour without falling off, and can be placed within that time in the camera. When I am going to take a proof at a distance, I moisten the sheet of lining paper with a thick solution of gum arable, and can thus preserve for a longer time its humidity and adhesion. I can also in this case make use of two glasses between which the paper is placed, according to the direction of M. Blanquart Everard; but it is necessary to take great care that the plates of glass are perfectly clean, and to have them re-polished if scratched. I employ for tins purpose, blotting-paper to clean them, as well as my plates ; it is much superior to linen, and absorbs liquids and impurities that adhere to it. , I never spare the blotting paper, for I would rather use a leaf too much than be uncertain about the cleanness of my glass. When the sheet of lining paper adheres well to the glass, it should not be removed, but only moistened afresh with water, after which you may apply another sheet of the sensitive paper. In preparing several sheets of the sensitive paper at a time, it is not necessary to wash the slab for each sheet ; you need only