Electro-medical instruments and their management : and illustrated price list of electro-medical apparatus / by Schall & Son.

  • Schall & Son.
Date:
1911
Catalogue details

Licence: In copyright

Credit: Electro-medical instruments and their management : and illustrated price list of electro-medical apparatus / by Schall & Son. Source: Wellcome Collection.

    188/252 page 172
    the clearest negatives and most details. Development can be prolonged very much with glycin without producing fog. Glycin is also the most suitable developer for the so-called tank development, which offers great advantages for our purposes if it is not important to examine a plate at once. Place the plate in a clean tank, preferably in an upright position, cover it with glycin developer, to which 20 times the usual quantity of water has been added, cover the tank with a lid to exclude the light, and leave the plates in for about an hour, and then examine them. All the details which can possibly be brought out will then be visible, and there is no danger that the plates will be too dense ; on the contrary, they will frequently be too thin. In this way it is easier to bring out all the details which are in a plate ; the most beautiful or perfect negatives which it is possible to obtain can be got with the tank development ; it is the best method of bringing as much as possible out of a rather under-exposed plate, and as no long expe- rience is required if done in this manner, it can be left to assistants who are not yet experts in photography, without fear that good plates will be spoiled by unsuitable development. Intensification.—Many X-ray negatives will be thin and wanting in contrasts. If there are details, however faint, such plates can be greatly improved by subsequent intensification. It is quite an easy process, which can be carried out in daylight. The intensification does not only increase the density, it considerably alters the character of the plate by increasing the contrasts and making the picture harder. If, however, the details are wanting on account of under-exposure or unsuitable development, subsequent intensification cannot bring them out, and will be of no help. If the plates are to be intensified, it is very important that they have been thoroughly fixed and washed, otherwise stains might be produced. As most medical men have experience in photography, it is not necessary to give lengthy instructions as to the development, printing, etc., here ; they can be found in the numerous books on photography. Examining the Plates.—If negatives are compared carefully with prints, it will be seen that some of the finest details are invariably lost by the process of printing on paper. The plates ought to be examined directly. This can be done either by placing them against a window covered with a ground glass, or better still the plates are examined by artificial light in a dark room. Two to four incandescent lamps are placed in a box behind a thin porcelain plate, and the negatives are placed in front of this plate. It is desirable to have a rheostat to control the amount of light, because thin negatives show to best advantage with a weak light behind, whereas for dense negatives a strong light is necessary.
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