Exposure. The length of the exposure varies considerably according to the sensitiveness of the emulsion; generally, one or two seconds are sufficient to take a well-lighted view. In the glass-house, where care must be taken to avoid contrasts, and to throw the light uniformly upon the subject, the exposure varies from three to six seconds. In thirty seconds we may obtain a very good effect, even when the light is so weak that it would be impossible to obtain a portrait with wet collodion. Make use of a shutter, especially for outside work; as, with the rapidity possessed by gelatin, it is indispensable that the foreground should be exposed a little longer than the distance. In twenty minutes it is possible to obtain an interior lighted with gas; and the prints, by contact, may be made by lamplight.
Concerning instantaneous work, for which gelatino-bromide seems to have been invented, more further on.
Gelatin plates may be exposed just as well when reversed as in the ordinary position, care being taken when focussing to consider the thickness of the plate, or to use a plate-holder made on purpose to correct the difference.
bles may be avoided by rinsing the plates with water before development, or by a gentle movement of the pan during the same. They can also be removed by a camel's - hair brush at the same time. Irregular lines and spots make their appearance when there is too little developing solution flowed over the plate, so that portions only are covered. In this case, also, if the plate be previously moistened with water, a less quantity of developer will be required. - W. P. Bolton.
830 One of the great claims in favor of the gelatin-emulsion process was and is its great rapidity. Every manufacturer of dry plates calls them "instantaneous," and undoubtedly they are so, provided the lens, its aperture, the amount of light, the nature of the subject, etc., allow of "instantaneity." Unfortunately, however, the cases which admit of instantaneous exposure (whatever the real signification of the expression may be) are very few, and not often met with. It is not so very long ago, however, that a doubt on this subject would have been considered heresy, and that the unfortunate proposer thereof would have been condemned for his ignorance. Not a few would have made us believe that the same description of lens, which, with a given diaphragm, would give an instantaneous pic-.ure on a 41/2 by 3 1/4 plate, would perform the same feat on a 10 by 8 plate. Four p. M. in June, or in November, a sea view or a dark forest - every subject was to be taken instantaneous; we could not work quick enough. I think experience has already shown the fallacy of those statements, and nearly every number of the News contains some sort of warning on this score. As I wish to endorse these warnings, I beg at the same time to give my brother-amateurs the reason why. In order to obtain a perfect gelatin negative, I have observed that the development must not take too much time. Pyrogallic acid - either used with ammonia and a bromide, or with ferri-cyanide and ammonia - is apt to stain the plate wherever manipulation of pyrogallic acid may decide to give it the preference, especially for landscapes, as his prints will have more delicacy and clearness. 332. These two developers are to be used in the following manner: At the exact moment of developing pour into a black dish made of hard rubber or pasteboard, for a half plate (13 x 18 centimetres) (five to seven inches), 50 c.c. (one fluid ounce five fluid drachms) of the iron bath which you use for the wet collodion, namely:
331. Development.. - And here is where genius in most needed. It is important that the development should be made in a large and cool room. If yours is not of this kind, take the precaution to place in cool water the solutions which are to be used in developing and fixing the image, and use for the washings water as cold as possible. On the question veloping the gelatino - bromized plates, the opinion of photographers is equally divided - some will only use the iron developer, others ,pyrogallic acid. It is well to have ready both of these developers, as each one sesses its particular advantages. Iron is without doubt the most certain and the easiest to use , but the operator who understand - thoroughly the the development has taken too long in consequence of too short exposure. And, moreover, I have experienced that with the ferri - cyanide, under these circumstances, the plate almost refuses to fix in the shadows, producing partly red or yellow fog. With the oxalate developer it appears that the development of under-exposed plates only proceeds to a certain point, and then stops altogether. As I only work landscapes, as a rule 10 by 8, it is of course necessary that the printing depth at the corners should be as good as in the centre, and this object I find impossible to attain where the exposure has been too short After fixing, the image, from a good negative in the middle of the plate, will merge into a fine positive at the sides. Intensification with bichloride of mercury will not do much good in these cases, for it seems as if this salt has a greater propensity to take hold of the well-developed parts of the picture, affecting the remainder less; and it should be well borne in mind that the mercury followed by ammonia strengthens, but does not develop. - H. L. T. Haakhan.
331. But the time taken in development has a great effect towards or against success. Take gelatin plate, expose on any subject, each half equally, and then cut the plate. Develop one-half in a given quantity of developer of the strength requisite to complete the development quickly; then develop the other half in the same quantity of water, but adding the reagent little by little, taking some time to acquire the same strength of developer as was used with the first half. You will find the slowly - developed plate will give a negative much denser and more brilliant than the quickly - developed one. From this it results that for a subject wanting in contrast, or a little over - exposed, it is safer to develop slowly; while a highly -contrasted subject will be the better for a development short and sharp. In whatever form you keep your stock solutions, have ever at hand strong solutions of ammonia, pyro-gallin, and bromide. I use the same stock solutions - pyrogallic, glycerin, and alcohol; ammonia, bromide, glycerin, and water - for every kind of gelatin plate. When I get a new make of emulsion, I never dream of making up my developer by the maker's formulas; if I did so, the facility of comparison would be lost. Stop development when there is no longer any pure white to be seen on the face of the plate, and when the high-lights can be seen at the bark. This rule, however, does not hold good for every kind of subject: practice in this matter is the best guide. you must have enough light to see clearly what is going on on the plate, and, what is more you must scrutinize carefully each change that takes place.