In preparing the albumen, take seventeen newly-laid eggs (eggs a week old are the best), break them, and carefully separate the yolks from the whites; take out the germs (treadles). Weigh out five grammes of iodide of potassium, one - quarter gramme iodine, mix therewith five hunded c.c. of albumen, then pour into a large basin and whisk into a froth; this is allowed to remain twenty-four hours in a cool place to settle down; the product is then filtered through a piece of clean linen, and is then ready for use.
Cleaning of the glass: It can be easily understood that the first condition to obtain a pure and perfect image is to cleanse the surface of the glass from all impurities. This is done by plunging, first of all, the glass in a strong solution of potash; it is then well washed and left for a few minutes in a tray containing water slightly acidulated with nitric acid; it is then well rinsed and wiped dry with linen towels. Take fine whiting and with water make a thick paste, and wipe or spread it all over the glass and allow it to dry, then rub it all off with a piece of fine linen. A few grains of talc (I mean as much as would lie upon a pin's head) are now put upon the glass, and rubbed over it in every direction with a piece of wash-leather. A badger-brush is now drawn over the surface, and the glass is ready for coating lovely results. A great many persons fail with lantern slides who make excellent negatives. The greatest judgment is required in the matter of exposure and development. It is impossible to save an over-timed transparency, and an intense one is of no use in the lantern. As to the emulsion method, refer also to Lesson U.
Coating the plate is considered by all as the most difficult operation. This must be done in a room set apart for the express purpose and free from dust. The best manner of operating is to take up by a tube the exact quantity of albumen required for each plate; breathe upon the glass, and let the albumen run out of the tube; take a clean glass rod and equalize it all over the surface, and then put it into the cupboard, upon the levelled glass shelves, to dry in the manner as previously described. The plates thus prepared can be kept for years.
Nitrate of Silver,.........................
Glacial Acetic Acid,.........................
After the plate has remained about a minute, it is taken out of the bath and plunged into a tray containing distilled water; it is then thoroughly washed in ordinary water and left to dry. After a time the silver-bath becomes tinted through the organic matter dissolved out of the plates. This color can be taken away by the addition to the bath of some chloride of silver or silicate of alumina (kaolin). This coloration does not exercise any bad effect, according to the opinion of several manipulators.
Exposure and developing: If the plates are intended for stereoscopic transparencies, lantern slides, etc., the negative is put into a printing-frame, and the prepared glass upon it. It is then exposed to a diffused light for a few seconds, and then taken into the dark-room to be developed; naturally, the camera can be employed for the same purpose. The development of these plates is long and tedious. A solution of gallic acid is made warm and the plate plunged into it:
500 c. c.
Acetate of Lime,.........................
The plate is left in this solution until the liquid becomes cold, a few drops of a solution of silver nitrate are added, and the image makes its appearance. More nitrate will intensify rapidly.
Toning glass transparencies is necessary to give them the pleasant appearance they bear. To have a beautiful purple color, they are toned in a chloride of gold bath. To procure a very agreeable sepia color, they are plunged into a weak solution of bichloride of mercury, and then, after washing, into a chloride of gold bath. Fix in hypo, either before or after toning. - Pbof. E. Stebbing.
There is no doubt but what the emulsion method will, in time, become the favorite one for making slides. It can be used "dry" when the positives are to be of the size of the negative, or "wet" when a change in size must be made, requiring the use of the camera. The best foreign slides are made by a kindred process, and they are superior to all.
It is now between seven and eight years since I exhibited before the South London Photographic Society some plates - both negatives and transparencies - I had at that time prepared, and which, I believe, were the first publicly shown produced by the gelatin process. I still have some of these specimens by me. They are quite as fresh and as brilliant as when first made, and the clear parts are as clear as the glass itself. This, I think, proves there is little amiss with the process. I will now endeavor to point out the causes of failure. One of these arises in the preparation of the plates, and to those who are interested in this branch of work my advice is, Do not aim at making very rapid plates. Great rapidity in transparency work leads up to failure; the slower the plate the more certain and more brilliant will be the result When I say the fraction of a second is quite exposure enough with even a slow plate, I fancy I hear some one say, " Well, the plates cannot be very slow." Well, perhaps not, if compared with the old collodion dry plate; but we are not now dealing with collodion but with gelatin, therefore the conditions are all altered. I believe it is from not fully appreciating the necessity for rapid exposures that so many fail in transparency work. The exposure has been too long - the result, thin image and fog; and when this occurs by no, possibility can a presentable transparency be obtained. The most expeditious and certain way to make transparencies is to make them by contact. If necessary to enlarge or reduce the image, then, of course, it must be done in the camera. In most negatives there are some portions that may be made use of for lantern sides. In this case all you have to do is to cut a mask in black paper the size you require for your lantern slide, put the negative into a printing-frame, place the mask in position, then the sensitive plate, close the frame, cover the front with a piece of cardboard, take it into the light, uncover and cover again as quickly as possible, giving only the fraction of a second for the exposure. I am now supposing we are working by daylight. If by gas or a paraffine lamp, hold the frame about six or eight inches from the flame, and give from one to two seconds, according to the density of the negative used. When exposed, the development may be the same as in my instructions for negatives, with either the alkaline pyro or ferrous oxalate. After development well wash, and then flood the plate with acid pyro and silver (see also instructions for mixing). The pyro and silver is only used to give a bite to the gold in toning. Again well wash after the pyro and silver; then flood the plate with a fifteen-grain solution of chloride of gold in water - gold twelve drops, water one ounce. Keep this moving over the plate until the required tone is obtained, again wash and pour over the plate a very weak solution of cyanide of potassium; wash and dry. If the cyanide be not used, the plates will after a time present a beautiful pinkish tint in the transparent parts, which in some subjects has a very pretty effect. After the first fixing in hypo all the rest of the operations may - in fact, should - be carried on in the light, as in that case you can see exactly what you are about. It is always better when preparing lantern slides to cut them to the size before coating. This prevents all risks of their being spoiled by cutting after the transparency is finished. - R. Kennet..