In photographing books in libraries, Herr Fassbinder adopts an ingenious device, which will save a great deal of trouble. The camera is fitted with the reversing mirror, generally adopted in the photo-engraving processes, which allows of the open book being simply laid on a convenient shelf below it, and the page kept flat by weighted lengths of silk. The originator uses bromide paper, which gives white lines on a black ground. For ordinary copying purposes the plate would have to be inserted in the dark slide, glass side outwards.
Photographs are usually copied under the same conditions as engravings, except that ordinary plates, or those of medium rapidity, are employed, and are developed carefully in order to retain as much soft detail as possible. Bromides and platinotypes seem to give the best results with photomechanical or slow lantern plates. Many operators prefer to copy a bromide print while still wet - that is to say, squeegeed on to a glass plate and surface-dried with blotting paper.
Framed pictures sometimes have to be copied in situ, hanging on the walls of the gallery. The camera must be slanted to as nearly as possible the same angle from the perpendicular, and exposure assisted with flashlight. But the results are not likely to be satisfactory. Oil paintings are best copied in sunlight, and the exposure, even under these conditions, is often a very long one. Isochromatic plates must be used, and, by daylight, the yellow screen for both oil and water-colour pictures. With an oil painting the varnish, brushmarks, cracks and other inequalities of the surface create most injurious reflections, and in some particular directions these irregularities are very strongly marked, and especially in diffused light. For this reason, unless direct sunlight can be secured, gas, oil, or arc lamps focussed directly upon the surface of the picture should be chosen. The lens can be worked at a comparatively large aperture.
These, we find, give the best results when the light is not too strong. A yellow screen is often not necessary, but an isochromatic plate must be used.
The documents must be photographed by as powerful a light as possible, direct sunlight, or the light of an arc lamp. A faded inscription usually takes the form of faint yellowish markings : these, Dr. R. A. Reiss recommends, should be brought out by a blue filter of ammoniacal sulphate of copper solution in a glass cell. A gaslight paper will allow of these marks being further intensified. Repeated reduction and intensification of the negative is another valuable method. Each stage will mark a further degree of contrast.
The following methods were recommended by Mr. H. Nolan in a recent article in the British Journal of Photography.
1. Finger-prints in dust: (a) On colourless glass; illuminate by transparence with oblique light; dark background : (b) On dark surfaces (a very easy subject); illuminate by direct light.
2. Finger-prints in grease (ordinary finger-prints). (a) On light surfaces such as china plates; dust on (dry) very fine graphite powder; blow off with bellows, etc., not with breath. The "dusting on" is best effected by charging a heavy flat-ended camel-hair brush with the powder, holding it near the surface, and jerking it by a blow on the hand which is holding it. (b) On dark surfaces, such as the black or green paint of a safe, mahogany furniture, etc.; treat similarly, using fine, dry whitelead powder. (c) "Invisible" finger-prints on paper. Develop with aqueous solution of silver nitrate (5 to 8 per cent.).
3. Finger-print in blood on dark surfaces (e.g. black bottles). In dark room illuminate by direct rays of arc or magnesium light, preferably concentrated. One may get reflections, but the pattern of the papillary ridges will stand out clearly.
Several methods have been suggested for reproducing medals and coins. The easiest way in the end, perhaps, is to photograph a plaster-cast, stained to a shade that will correspond with the metal of which the original was made. Another way is to spray the medal with grey colour from an airbrush, or to smoke it over burning magnesium ribbon. Some have tried with success a single swinging lamp as the source of light, thus destroying reflections. At the L.C.C. School a special method has been devised by Mr. W. I. Smith for fastening the medal on the easel. An aperture is cut out of millboard corresponding roughly to the shape of the medal but a little smaller. It is then cut in half, the medal is laid down on the copying board and one half of the millboard placed on each side of it. These can be wedged up closely and pinned down with drawing pins, so that they hold the medal safely.
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.