Photographic emulsion

“ Can the same speed, contrast, and color sensitiveness be obtained on film as on glass? Is the picture so obtained as permanent or reliable as the plate image?
It must be confessed that up to the present emulsions on film have not proved the equal of those on glass. It has been found by emulsion manufacturers that the same emulsion flowed on film and on glass gives better quality on the glass. Emulsions specially prepared for film fall somewhat short of the best plate emulsions. ”

“ Vogel has recently introduced an emulsion made with acetic acid, gelatine, pyroxyline, and bromide of silver, which is very clean and very fairly rapid. Plates are more readily coated with it than with gelatine emulsion, but less so than with collodion emulsion.
Another very decided advance in photography is the doing away with glass as a support for the emulsion. Mr. Warnerke has perfected a process by which the photograph is taken on paper instead of on glass. He has a sensitive tissue which can be made of any length, and can be rolled on a roller and exposed in the dark slide. ”

“ The Image is "Flat," or shows comparatively little contrast between the highest lights and the deepest shadows. This may, of course, be due to the absence of contrasts in the subject photographed; it is commonly due to over-exposure; it may be caused by using a developer containing too little reducer, or restrainer, or both, and too much alkali; sometimes it arises from a defect in the quality of the emulsion, or from the fact that the plate has been coated with an abnormally thin film of emulsion. ”

“ Further experiments taught me that even if 60 to 80 c.c., and more, of these coloring matter solutions were added, and the emulsion was left to coagulate and then laid in alcohol for several days, after which it was washed well, so that hardly any coloration could be observed, it showed, when making a copy of an oil painting, that the color sensitiveness of the emulsion was not reduced, and that it had rather increased in relative sensitiveness. ”

“ We can put these emulsion plates and carry them off where we please, and, what is still more important, we can put the emulsion upon very thin material, and I have here (exhibiting them) thin sheets of celluloid upon which this emulsion has been spread and pictures taken. That is not all, either; they can make it still thinner (producing small camera) they can put it on a roll and in this camera is one of those rolls, and in that box I can take a hundred pictures without reloading the instrument. ”

“ Since the emulsion process has taken root, no improvement has awakened such a lively, steadily increasing interest as photography of colored objects in their correct tone proportions; a process which makes it possible to reproduce the warmer color-tones, particularly yellow, orange-red, and yellow-green, in their correct light value as they appear to the eye. ”

“ Another pin will secure the second end of the film. The drum is an inexpensive and very handy accessory to the moving-picture photographer, especially in the drying operation, when forceful methods have to be adopted.
Unfortunately the drying of the film cannot be accelerated to any great extent. The hardening of the gelatine emulsion cannot be hastened, as in glass plate work, by immersion in a bath of methylated spirits or some other evaporative agent, since the alcohol contained therein would dissolve the celluloid base. The only available means is a current of warm, dry, clean air. ”

“ An excellent method of preparing emulsions of resins and gum-resins, is to put the article into a marble or wedgwood mortar, and to pour over it about 4 times its weight of rectified spirit, which is then to be ignited, and the mixture triturated until an equal consistence is obtained. The liquid is then to be added gradually, and the whole patiently triturated or shaken until cold. Yolk of egg or mucilage may be added to the fluid resin or gum-resin, if desired, as in the common method, but an excellent emulsion may be made without them. ”

“ A camera, then, consists of a light-tight box having at one end an arrangement for holding a lens or a card with a needle-hole in it, and at the other end a device for holding some light-sensitive chemical to receive the image projected by the lens. In modern practice this light-sensitive chemical is almost always bromide of silver or a mixture of the bromide with other silver compounds, these chemicals being held in an emulsion of gelatine. When the gelatine emulsion is coated in a thin film on a sheet of glass the result is known as a dry-plate, or, simply, a plate. ”

“ Emulsify it with a few cubic centimetres of distilled water in a watch-glass, by gently moving the spatula to and fro in the water. Do not rub up the growth on the side of the watch-glass. Some workers prefer to use tap water, others employ normal saline solution, but distilled water gives the best emulsion.
3. Spread a thin film of the emulsion on a newly flamed cover-slip, using no force, but rather leading the drop over the cover-slip with the platinum loop. ”

“ This extreme fineness is secured by long emulsification, or by the use of ammonia and a boiling heat.
The strength and tenacity of the emulsion depend on the quality of the gelatine, and its freedom from deterioration during the process of emulsification and the subsequent washing. A soft gelatine is suitable for the process of emulsification; afterwards a hard quality is used to give body and resistance.
The presence of free bromide or of free nitrate of silver in the finished emulsion would be fatal to its usefulness ”

“ This emulsion-like mass is brought on to the paper by the machine, not the ink alone, as in collotype, the chromated film of which holds only that moisture which is requisite for its swelling, while its support, the glass, can retain no moisture. It is also the fact that the amount of moisture in the collotype film is so small that the formation of this emulsion practically does not occur. From these comparisons and explanations it also follows that the printing technique of the two processes must differ. ”

“ No general rules can be laid down; the appearance of the properly developed image depends on the thickness of the film, the granularity of the silver salt, the presence or absence of silver iodide, and the composition of the emulsion used. Experience only is of value, and the best way to secure uniformly satisfactory results, is to keep as far as possible to one brand of plates. With some plates, for example, very little of the image should appear at the back of the plate, with others the greater part of the image must be distinctly visible there. ”

“ Since the distortion of the photograph arises from the unequal expansion of the paper when wet, it becomes a question whether something may not be done in the selection of the paper itself. It may be that some makes vary much less than others in the "length against width" extension of the surface by wetting. It must be remembered that for gelatine emulsion we are not nearly so limited in the selection of paper as when it is required to be albumenized. ”

“ So it behoves the worker to keep his dark room and drying room free from dust. Drying should not be done in the dark room because there are small particles of chemical dust always floating about in such surroundings. If these should settle upon the emulsion they would play sad havoc with it.
When the gelatine has hardened the film may be transferred direct from the drum to a spool by means of a winder. When the beginner has become expert he will be able to do this by hand, but it is never a wise practice since the coating is liable to become scratched. ”

“ The previously-formed saponaceous mixture is now to be placed in the mortar, and the ready-formed emulsion in the runner; the soapy compound and the emulsion is then carefully blended together. As the last of the emulsion runs into the mortar, the spirit, in which the otto of roses has been dissolved, is to take its place, and to be gradually trickled into the other ingredients. A too sudden addition of the spirit frequently coagulates the milk and causes it to be curdled; as it is, the temperature of the mixture rises, and every means must be taken to keep it down ”

“ Today these observations have become of the greatest importance to practical photography. They have led to the preparation of the silver bromide gelatin emulsion and the silver bromide gelatin plates, which are twenty times more sensitive than the silver iodide collodion plates, and have become indispensable when impressions are to be taken in a dim light. ”

“ The developing and printing rooms in a large film-picture factory are highly interesting hives of activity. Large troughs and tanks containing the various solutions79 are on every hand, together with adequate supplies of running water. Everything, of course, is carried out in semi-darkness, the only light available being that emitted from ruby lamps. The fixing solution after it has served its purpose is not thrown away, but is subjected to a chemical treatment to recover the bromide of silver which the hyposulphite of soda has dissolved from the sensitised emulsion on the film. ”

“ Soak the glass in strong lye or potash for a time, then wash carefully and put into acid, then wash p47 again and albumenize with the white of one egg to six ounces of water without ammonia. The plates should be slightly warm when being coated.
COATING THE PLATES.
Hold the plate in the left hand, as you would for coating with collodion, flow with emulsion as you would with collodion, letting the surplus flow off the right hand lower corner, but do not let more than the gross surplus run off; retain enough to make a rather thick film ”

“ Of the alkalies, the volatile in its mildest state, or carbonate of ammonia, is the only one which can be safely used in removing dust, oil, and varnish from a picture, which it does powerfully, it must, therefore, be much diluted with water, according to the power required, and employed with judgment and caution, stopping its action at the proper time by the use of pure water and a sponge. A thick coat of wet fuller's earth may be employed with safety, and, after remaining on the paint a sufficient time to soften the extraneous surface, may be removed by washing. ”

“ Moreover, the color does not again reappear after washing, as it does sometimes when the fixing salt has been partially washed away. In cases where there is great tendency to frill--such, for instance, as when a soft sample of gelatine has been employed, or old decomposed emulsion worked in with the fresh emulsion--it will in such cases be safer to put the plates in the normal-bath for a few minutes previous to immersing them in the acid bath. ”

“ This method, although a great improvement upon the older ones, yet leaves much to be desired, especially for those who are not in the habit of making emulsion regularly, but only an occasional batch. When the weather is at all warm it takes a long time for the emulsion to set, unless ice be used, and when once it is set the washing process is an exceedingly "messy" one unless the water be cooled with ice; and the amount of water taken up during washing is often so great that there is considerable difficulty in getting the emulsion to set on the plates. ”

“ Every amateur photographer in his earliest days has endeavoured to force the drying of a glass plate after development by placing it before the fire. Invariably the effort ends in disaster. The gelatine melts and causes the emulsion to run all over the plate, producing grotesque results.
In order to produce this bizarre film a primitive apparatus was contrived, consisting of a small tank the back and front of which were cut out to admit pieces of glass. ”

“ This sort of oily liquor, in which the oil is only divided, not dissolved, is called an Emulsion. The oily particles in Emulsions spontaneously separate from the water, when left at rest, and uniting into greater masses rise, on account of their lightness, to the surface of the liquor, which by that means recovers a degree of transparency.
If vegetables abounding in essential oils and resins be digested in spirit of wine, the menstruum takes up these oily matters, as being capable of dissolving them ”

“ The ideal emulsion for the damping agent is olive oil and soft soap heated and mixed together to form an emulsion, but the high cost of these commodities have placed them out of the reach of practical work and now various substitutes are employed. ”

“ The water distilled from the bitter almond, when strongly impregnated, has been found to exert a deleterious action on the human body, and to prove fatal to many animals. Solubility. By trituration with water a milky mixture is produced, (an emulsion) , for which purpose the sweet almonds should be previously freed from their cuticle, (blanched) , and this ought to be performed by infusing them in tepid water; for when hot it separates a portion of their oil, as is evident from their being thus rendered yellow, and the emulsion is therefore more liable to ferment, and be decomposed. ”

“ Experiments by Hillyer (loc. cit.) show, however, that while N/10 solution of alkali will readily emulsify a cotton-seed oil containing free acidity, no emulsion is produced with an oil from which all the acidity has been removed, or with kerosene, whereas a N/10 solution of sodium oleate will readily give an emulsion with either, thus proving that the emulsification is due to the soap itself, and not to the alkali. ”

“ He further, in August 1879, announced that he had obtained great rapidity by adding to the bromide emulsion a certain quantity of ammonia. This addition rapidly altered the silver bromide from its ordinary state to the green molecular condition referred to above. At this point we have the branching off of the gelatin emulsion process into two great divisions, viz. that in which rapidity was gained by long-continued heating, and the other in which it was gained by the use of ammonia—a subdivision which is maintained to the present day. ”