William de Wiveleslie Abney

“ Another reason is, that you can use a more powerful developer. If you separate bromide of silver which has been emulsified in gelatine, and place it in collodion, the extreme rapidity will be gone, for the simple reason that you can not use as strong a developer as you can with a gelatine emulsion; in fact, the property that gelatine possesses of acting as a physical restrainer comes into play: each little particle or aggregation of particles of the salt is surrounded by gelatine, which prevents the developer acting rapidly on them. ”

“ My advice to those who wish to make collodion or gelatine emulsion is, to add the silver to the collodion or gelatine, and then add the haloid salts afterward, and you will get as perfect an emulsion as you choose.
It is a great comfort in the collodio-bromide process that the operator is able to give local intensity (a most desirable quality in all artistic work) to the image. I do not believe any process is perfect until that power is placed in the hands of the manipulator ”

“ Another developer, which is competent to work also without a restrainer, but has not been used to a very great extent on account of its high price, is hydro-kinone. It is a much more powerful absorber of oxygen than pyrogallic acid, to such a degree that one grain of it, is as active as two grains of that substance. Not requiring any restrainer, even when so troublesome a salt as silver chloride is used, it is able to give a better detail and allow a shorter exposure in the camera than when the ordinary alkaline developer is used. ”

“ Without a restrainer, the tendency is for those parts to be first reduced, but the action extends to that which has not been acted upon by the light. It has been usually said that alkaline development is only available for bromide of silver, but my experience has taught me that iodide of silver is as amenable to alkaline development as the bromide, although not so rapidly, and that chloride is very amenable to it, and will give most beautiful pictures. ”

“ When you have silver precipitated from a solution by any means whatever, you have it always in a crystalline form, and, as all crystals possess polarity, so crystals of silver possess polarity; and where one silver particle is deposited, there another silver particle will deposit. ”

“ Monkhoven for the production of very sensitive gelatine emulsions by adding ammonia with the nitrate of silver. The ammonia process found many admirers, among them Dr. Eder, whose method of adding a large quantity of ammonia has given very sensitive pictures, and very vigorous ones when the sensitiveness is not too great. A process introduced by Mr. Cowan is even superior to that of Dr. Eder. He emulsifies his bromide in a very small quantity of gelatine with ammonia, and adds sufficient gelatine when the emulsion is ripened. ”

“ Wishing to reproduce an ordinary gelatine negative having the proper gradations of light and shade, he took a gelatine plate, immersed it in bichromate of potash, allowed the film to dry, and then exposed it to light behind the negative to be reproduced. In this exposure he had an oxidizing agent present in his film; the oxidized parts were acted upon by the light, leaving the other part intact; and by that means he got a reversed image. Oxidizing agents enable us also to get rid of fog. ”

“ One point that has exercised the minds of a great many photographers is the illumination of their dark rooms. [The lecturer having shown the relation of the several parts of the solar spectrum with the absorption properties of different substances used in photography, proceeded to demonstrate the effect of differently colored glasses upon the passage of rays, and announced his conclusions.] ”

“ If photographers want to have an absolutely safe light in developing their pictures, let them glaze their studios withc obalt glass and stained red, and they will get nothing but the light of that particular refrangibility, which will not affect any gelatine plate of the ordinary type. You may glaze and glaze with ruby, but you will never get rid of blue light entirely. ”