If the light tones are correctly represented on one of the partial images, and the shadows on another, it is a sign that the paper selected is not suitable for printing from that particular negative. The test should be repeated on a paper exactly suited to the negative. 2 If the shadows are correctly reproduced with an exposure shorter than that which gives the best rendering of the light tones, a paper which gives softer contrasts should be used. On the con trary, a paper giving greater contrast should be selected if the shadows are correctly rendered with a longer exposure than that required for the light tones. In either case, a test for the correct exposure should be made on the new paper.
The best exposure being known, any desired number of prints may be taken consecutively, and the development deferred to allow of the simultaneous treatment of all the prints from the same negative. An essential condition is that they should be developed in exactly the same manner as the test piece, the developer being identical in composition and temperature.
554. Urgent Prints. In certain cases, as, for example, current events for the daily Press, topical cinematography, military operations, etc., one or more prints may be required in the shortest possible time after exposing the nega tive. The print is then taken from the wet negative, either before or after fixing. It must be remembered, however, that the bromide of silver in the unfixed film forms an image com plementary to the negative, the contrast of the negative image being thereby considerably reduced. Also, a temporary fixing in an acid solution with a brief rinsing will require as much time as a thorough fixing in a fresh hypo bath of suitable strength.
Printing from a negative which has been fixed, very rapidly rinsed and surface-dried, is best carried out by means of the enlarging apparatus. If absolute sharpness is not essential, a print may be made by contact. The sensitive paper should be protected against actual contact with the negative impregnated with hyposulphite by the interposition of a very thin sheet of celluloid of ample size, applied to the negative with a squeegee. On account of possible want of con tact, diffused light should be avoided as far as possible. The image will be slightly sharper if the print is made at a long distance from a light as small as practicable, the frame and the lamp being kept perfectly still during the exposure.
In the case of a negative which has not been fixed but development stopped by means of an acid bath, 1 the sensitive paper may be applied directly to the negative by means of the squeegee (gelatine in contact with gelatine). The paper should be previously moistened with water and the exposure made in the usual manner after wiping the glass side of the negative, or after placing on a sheet of glass in the case of a film negative. It should be remembered that the sensitiveness of the paper is somewhat less when wet.
555. Soaking before Development. The devel opment of Punts on paper is considerably facilitated if they are wetted before development. This prevents the paper from curling in the developing solution, and also lessens the risk of air-bells forming on the surface, a risk to which rough papers are specially liable. It is very easy to ascertain if air-bells have formed by examining the print close to the light, and, if any are seen, to ensure the uniform wetting of the surface by passing a brush or a tuft of cotton wool (thoroughly wetted) over the whole surface of the gelatine.'
The same precaution is generally adopted with positive cinematograph films before devel opment (§ 369).
556. Development. A print on paper can be considered perfect only if development has been sufficiently prolonged to produce the strongest black 2 which the paper in use can give, without, however, being carried to such a stage that the whites are degraded. When it is desired to utilize only a part of the scale of tones, e.g. from white to a medium grey, as in portraits of children, mist effects, etc., the paper should be selected and the exposure regulated so as to produce only a grey under the thinnest part of the negative. But development should be carried as far as in the case of a print having full blacks. It is only on this condition that the intermediate tones can be correctly rendered. A curtailed development produces, as a rule, only greenish or yellowish images"—very un suitable for after-treatment—sulphide toning, Bronioil, etc. A very short development will even produce an irregular image, certain parts being more fully developed than others.
In order to ascertain the normal limits of the time of development 4 of a certain sensitive paper in a given developer, used at a definite tempera ture, it is necessary to find out what minimum time of development will produce the maximum black and at what stage of development the whites begin to veil or stain. These minimum and maximum times of development respec tively are ascertained as follows (Dr. B. T. J. Glover, 1922)— A strip of the paper to be tested is exposed uncovered in a printing frame, at a suitable distance from a source of light, e.g. for 2, 4, 8, i6, and 32 seconds respectively (§§ 552 and 553), adjusting the exposure so as to produce the densest black possible. This strip should be developed for 2 minutes if it i a bromide paper, or 30 seconds if gaslight, in each case using the developer best suited to the paper. It should then be ascertained which of the exposures has produced the most intense black. If this exposure should be either the longest or the shortest of the times given it will be necessary to repeat the test after bringing the frame nearer to or moving it farther away from the source of light. Assume, for example, that 8 seconds is the exposure which gives the densest black. A strip of paper about an inch or rather more in width should be exposed in a printing frame for the time dctermined,namely, 8 seconds, half of its width being covered with a length of black paper. This strip is then developed in a bath whose temperature has been noted, and pieces about an inch long are cut or torn off at intervals, care being taken to mark on the back of each the time during which it will be developed. These development times should form, preferably, a geometrical progression in a lesser ratio than that used for ascertaining the time of exposure. The following series of num bers may be taken as an example of suitable times of development in i8 25 35 50 70 100 140 200 280 the first six being appropriate for gaslight papers and the last six for bromide paper, for the pur pose of this experiment.