The emulsioo may now be scooped up with a glass spoon, and melted in a porcelain jar at 32° (92" F.). This is best effected in a water-bath. The emulsion is now ready for coating the plates ; 1 oz. of fluid should ooat 1 doz. plates 41 x 31 in. All the operations described after mixiag the salts with the silver must be conducted in the dark room. As a further security against light, the dark room should be illuminated by a paraffin lamp, enclosed in panels of ruby glass, covered outside with orange paper.
In ooating the platea, it iB neceesary to employ a table of plate-glass (Fig. 1094) carefully levelled. The emulsion, when dissolved, should be passed through a sieve of fine muslin, to remove grit and mechanical impurities. It should then be de canted into a wide-mouthe,d bottle, half covered at the mouth with a membrane of muslin, which inter cepts air-bells in pouring on to the plate. The addition of 2 oz. of alcohol to the pint of emulaion will cause it to flow more freely over the plate, aad the plate to dry more rapidly when set. When the emulsion has been poured over the plate, spread with a glass rod, and the excess drained off, the plate may be placed upon the level table to set. When set, it ehould be reared up in a rack to rlry. Under favour able conditions, drying will be completed in 8 hours.
Plates made by this proem are ao rapid as to render the use of the " drop shutter " necessary for out-door work. It must be underatood, however, that what is termod " instantaneous photography " is only possible under favourable conditions of light and atmosphere. It ie impossible to set down any arbitrary rules to guide photographers in timing exposure of gelatioo or any other plates. So much depends on the conditions under which photographs are taken. For instance, plates pre pared by the above formula may prove at one time more rapid than at another, owing to the emulsion being boiled for a longer or a shorter time, or to the salts being mixed at a higher or a lower temperature. The focal length of the objective, and the aize of the diaphragm em ployed, na well as the light under which the photograph is obtained, are all factors to be taken into account in determining duration of exposurf3.
Assuming that the plate has been properly timed in the camera, it may be developed with the following alkaline pyro-eolution :—(a) 6 gr. pyrogallio acid, 2 oz. water ; 1 oz. ammonia liq., 2 oz. distilled water, 60 gr. potassium bro mide. Place the exposed plate in a shallow ebonite or porcelain tray, film uppermost, pour over solution a, and see that the plate is quite sub merged. Drop into a glass measure font to six drops of b ; pour hack a into the measure, and again
flood the plate by pouring back the developer. The negative will soon appear, and should be fully developed iu half a minute. Wash off the developer, and fix in 5 oz. eoda hyposulphtte, and 10 oz. water. After fixing, wash thoroughly with water, and then consign the negative to a saturated bath of common alum, which should remain for 5 minutes. Again wash and rear up to dry. Heat must not be applied in drying, otherwise the gelatine will run. Drying may be greatly aided by pouring methylated spirit over the plate; when draining, it carries the water with it.
Iatensify the negs.tive, if necessary, with 20 gr. pyrogallic acid, 25 gr. citric acid, 6 oz. water. When required for use, to 1 oz. of this, add 4 min. nitrio acid, and 20 of a mixture of 30 gr. silver nitrate, 1 oz. distilled water. This is hest effected after the negative is dry, and thoroughly freed from hyposulphite, when it must be rnoistened in a tray of water, aad the solution be poured over. The operation must be conducted in the dark room. When fully intensified, wash off, dry, and varnieh, as in the wet collodion process. The gelatine plate, when dry, may be heated without risk of injury.
Retouching Negatives.—Although retouching is a sort of pseudo-art, and has nothing to do with the ecientiflo phase of photography, it is nevertheless important, seeing that a poor negative by dint of pencilling, may be made to produce fair prints. A really good negative may also be improved by a few well-placed touches of the retoucher's pencil.
The negative to be dealt with should be set upon a table-easel, furnished with a white reflector, whioh throws the light up through the negative, revealing its flawa and defects. The varnish on 5 r 2 the negative should be perfectly hard and dry. The portion to be retouched should be rubbed with the soft point of the finger, and a little finely-powdered pumice, so as to impart a tooth.to the surface. The pencils used, FIB and BB, should be sharply pointed. With the first, if it be. a portrait-negative that is on the easel, touch out freckles or transparent spots on the face. With the BB, come lightly over the hard shadows about the mouth, nose, and eyes. But above all things, care must be taken not to overdo retouching, as it is apt to interfere with the true characte. r of the face. Artistic perception, and a kindly appreciation of character, are valuable attributes in the professional retoucher.