Printing The Positive. The gelatin negative being more opaque than the collodion negative, in order to judge finally the degree of intensity necessary to give it to obtain a good positive print, it is indispensable to make some previous trials on paper. A good gelatin negative, like one. .....
made with collodion, should be brilliant, rich in details, full of relief, very strong, but at the same time the lights should be transparent The gelatin process lend - itself marvellously to obtaining a negative which certainly could not be produced with the game qualities by the wet - collodion process. For printing the negative, if Is necessary to use the customary precautions and means to retard or increase the action of light on those portions of the negative that might require them.
335. Next to good gelatin plates is a good varnish to protect them from the weather. Damp is known to spoil them quickly, and a varnish that has the following qualities is a good one: First, that it shall perfectly protect the gelatin film from damp; secondly, that it will not become tacky and stick to the printing paper in the hottest sun; and, lastly, that it can be removed without danger to the film, if it be required to strengthen a negative that is considered to be too weak after varnishing. The formula I give below will do all these.
Take methylated spirit thirty ounces, place it in a stone bottle and add one ounce of shellac; then place the bottle in hot water for fifteen minutes, and well shake. Next add gum-sandarac two and a half ounces, well powdered, and gum-benzoin two ounces. Shake well at different times for a few minutes, and let stand a day. Then filter, and it will be found to make a varnish that will flow well and possess the qualities I have described. - George Willis.
336. Print farther or darker than wet plates, and do not tone so far as prints from wet plates. My printing - bath is as follows: Silver, sixty grains to one ounce of water; to this add nitrate of ammonia until the solution indicates eighty grains; make the bath slightly acid in cold weather; float from one and a half to two minutes; fume forty minutes.
837. Although the instructions so far given are rather lengthy, it may be necessary to render them still more complete by adding the following remarks, the importance of which will certainly not escape those who have already practised this new process. For gelatin work, we may, in fact, it is even necessary, use more light than is generally done. It if essential, to make good work, to see very clearly what is being done. The fog which sometimes occurs, does not arise, as much as it is supposed, from
My toning - bath consists of acetate of soda, one hundred and twenty grains; nitrate of uranium, fifteen grains; water, sixteen ounces; neutralize gold one grain to an ounce of water; also neutralize the uranium.
It has been stated that dry plates would not stand the heated term of the summer season. I can certify that they will stand the heat, as I have tested the same to my entire satisfaction, having exposed them with the thermometer at 104° in the shade, and they developed perfectly clear, and where a wet plate would dry and fog from the heat. - C. F. Moelke.
887. Fogging invariably makes its appearance when the emulsion is prepared with an excess of silver nitrate. Many kinds of gelatin are liable to give fog when they have an alkaline reaction. Fogging is also caused by continuous digesting at too high a temperature, by the addition of too much ammonia, or by too long or too great heating with the same substance. It may be cured by adding bromide of potassium or a few drops of the tincture of iodine. Emulsions which are inclined to fog are best cured by being washed first with a dilute solution of bichromate and then with water. Due attention must be paid to the mixing of the ingredients in the required proportions, and at the proper temperature. By the addition of ten per cent, of alcohol, the bromide of silver is brought to a pale condition. In employing bromide of potassium it must be chemically pure; by using it in excess of the silver , a much more sensitive emulsion ensues. As to the quantity of gelatin in the more fluid emulsions, the bromide of silver is granulous and green, and, unless care be taken, likely to separate out, while with a larger amount of gelatin it is finer and paler. With regard to the quality of gelatins, those of Nelson's are the purest, although not so firm as others - Swinburne's, and those of French and German manufacture, for instance. Imperfect washing often gives hard, impure negatives, while thorough and continuous washing greatly improves the emulsion. - Dr. D. Von Monckbove 19 an excess of light in the dark - room. The important point is that this light should he of a particular nature. It should he of a decided red, or ruby color. To avoid fog, the attention of the photographer should be directed especially to the choice of a good emulsion, to the careful examination of his chemicals, to his camera, and principally to his holders, into which the least trace of light should not penetrate. It is well understood that this applies also to the dark-room. A large black cover over the tube of the objective, the camera, and the frame, is also indispensable, especially fur outside work. The operator should not forget, also, when developing, to measure the quantity of bromide by the sensitiveness of the emulsion and the time of the exposure.
338. Nelson's gelatin No. 1 appears to be the best for making the emulsion, but in summer especially it is well to add to it a firmer gelatin which sets more readily; several French gelatins possess this quality. The addition of fish-glue presents also certain advantages; it gives more permeability to the film, more sharpness, and a more agreeable color to the negative. To obtain a good emulsion easy to follow by transparency during development, the coating should not be too thick, and the weight of the gelatin should be the three-fourths of that of the bromide of silver. For easy manipulation, the best proportion to observe between the bromide and the silver is that of two to three.