Dr. E. Demole has illustrated the catalogue of the Numismatic Society of Geneva by a very ingenious process. The coins or medals are placed between two sheets of thin white glazed card, and damped. The whole is put between two pieces of thick felt and submitted to strong pressure in a copying press. The impressions are then lighted from one side, and photographed on to smooth glazed bromide paper. As the cardboard impression reversed the lettering, the result is a true positive, and owing to the shadows cast by the side lighting, a good representation of the essential features of the coin.
Highly polished metallic surfaces, especially silver, must either be dulled by immersion in ice-cold water, or dabbed over with fine white powder. Brasses or other engraved metals are generally smeared over with putty. The lighting may sometimes be contrived from one side, so as to diminish the reflections from the polished surface. Glass vessels are filled with some yellow or faintly pink liquid, and the interstices of the engraved pattern filled in with French chalk, and afterwards dusted to remove the chalk from the rest of the surface.
Duplicate Negatives.—The best method is to make a transparency by direct contact in the printing frame, either on a photo-mechanical plate or the slow lantern plates which may now be obtained in all sizes for the purpose. From this any number of new negatives may be made, using the same kind of plates as were employed for the trans parency.
Reversed Negatives.—A reversed negative is a great saving of time in the carbon process and is useful for many photo mechanical operations. Such negatives are made (1) from transparencies in the enlarging lantern, (2) by photography with the reversing mirror, or by putting the plate in the dark slide with the glass side uppermost, (3) by contact. Soak a dry plate for five minutes in a to per cent. solution of potassium bichromate to which an equal quantity of methylated spirit has been added. Blot off and dry in a dark place. When dry expose in the printing-frame in contact with' the negative to be copied until the image can be faintly seen through the glass at the back. Then develop in any alkaline developer, and fix as usual.
Another way sometimes recommended for securing a reversed negative is less reliable, but most interesting as an experiment in the reversal of the latent image. Expose
an ordinary dry plate (in the printing frame in contact with the negative) to diffused daylight for about 30 secs. being over too times the normal exposure. If development is carried on with ferrous oxalate or hydroquinone, a reversed replica of the negative will present itself. The reason probably is that prolonged action of light brings about a chemical change in the upper layer of silver salts which enables it to protect from further action the layers beneath it.
Theatrical Scenes.—Mr. Arthur Payne adopts an ordinary dry plate of medium sensitiveness bathed for three minutes in the following bath : Distilled water . . . . . . . Ltoo parts.
Ammonia (•88o) . . . . . . . 6 parts.
Orthochrome T stock solution (i : woo) . . 8 parts.
The bath is filtered before use, and the temperature about 65° Fahr. After bathing the plates are washed for three minutes and dried in the dark, preferably in a drying cup board. They should be used within a week or ten days of bathing. The sensitiveness to yelloW light is increased wonderfully by this treatment, frequently up to 50o H & D.
Mr. Payne has secured some remarkable successes with these prepared plates, which enable scenes in a theatre to be. photographed during the performance itself, without any alteration of the stage lighting. Some of these required only of a second at f/4. A longer exposure than this is of course desirable, and two seconds at f/8 would be a more general rule. The nearer the camera to the object, the shorter may the exposure be. For scenes of the whole stage, the worker may occupy a position in the dress circle ; for single figures at the side of the stalls.
Flowers and Fruit.—Studies of this kind are often to be accomplished by artificial light. Sprays of cluster roses look well on a background of black velvet. Dull-surfaced vases, etc., may be used for bunches of flowers or piles of fruit, and no sprays should be allowed to project too far forward, as the focus is necessarily short and the field of sharp definition a narrow one. Cardboard reflectors, bent into a concave semi-cylindrical shape, will mask the lamps and concentrate illumination upon the object.