Preliminary Preparation Of The Plates. The glass plates require a coating in order to make the emulsion adhere quite fast, and for this purpose a solution of caoutchouc or chrome gelatin is used. A. Coating with Caoutchouc. - Pour twenty-five grammes chloroform over one gramme soft, brown caoutchouc; let the whole stand quiet two or three days, stirring it occasionally, and dilute the solution with eight times its volume of light benzine, and filter through cotton. The solution keeps for months. With it the cleaned and dusted plates are coated the same as with collodion; the coating dries in five minutes. The drainings must not be poured back into the original bottle, but caught in a separate bottle, to be diluted afterwards with one-eighth benzine and filtered, before ready again for use. B. Coating with Chrome Gelatin. - Dissolve one gramme of gelatin in 300 grammes of warm water, filter, and after washing add six cubic centimeters of a filtered solution of chrome alum, 1: 50. The solution keeps from four to six days. The plates are acidulated, washed very thoroughly under rubbing, and then placed in a cup with distilled filtered water. They are then taken out one by one, a portion of the solution of gelatin is poured on and allowed to flow over the whole surface, when the excess is drained off. (These drainings are not used again.) The first affusion drives off the water, and after the same has drained off another coating is poured on, and the plates are placed in a vertical position for draining and drying. In not too cold temperature, they will be dry inside of an hour. In winter, the gelatinizing is-done in a warm place, as cold plates do not take the gelatin easily.
The Pouring on of the Emulsion. - Place the bottle containing the emulsion in warm water of about 40° R., until the emulsion, which sometimes congeals in the cold, becomes thoroughly liquid, and then pour it on like collodion. The substance flows and evaporates somewhat slower than collodion, so that no fears of drying need be entertained in pouring on. The plate may be balanced in the hand, so as to help to produce an equal coating.
While the excess is drained off, rock the plate, but slower than with collodion. When the last drop gathered on the corner begins to congeal, place the plate in a vertical position (298 ) taining bromide of silver, or its equivalent, with pyroxyline, which consists in first producing the gelatin emulsion to the usual way drying the same, than dissolving it in an organic acid and mixing the solution with pyroxylin also dissolved it in an organic acid. Thus it will be seen we have a collodion emulsion , so to speak, which must be difficult to prepare. But, since it is in the market and destined to become a to dry. The drainings are caught in separate bottles. The preparation takes place in the dark-room, with red light. For draining - bottles, collodion bottles covered with brown paper are recommended. The beginner may meet, perhaps, some difficulties at first, but after one or two experiments he will become quite an expert. In winter, a well-warmed room is indispensable.
The Exposure. - For exposure, light - proof cameras and boxes are required, also protection of the objective from lateral side - light. Time of exposure about one-third of the time necessary for wet iodine - co llodion plates. Exposed wet, the emulsion plates are a trifle less sensitive than when exposed dry.
Developing - For this stage of the manipulation, the simple alkaline pyrogallic developer is best adapted, but it is necessary to modify the same according to the temperature and character of the plate. For a carte -de-visite plate, 5x8 inches, take
Solution of Bromide of Potassium, 1:10,.....................
1 1/2 to 2 C.C
Solution of Pyrogallio Acid in Alcohol, 1:10,..............
Add five or six drops of ammonia, pour the mixture in a cup, and place the plate in it, with subdued light If the plate has been exposed wet, it must be previously placed in a cup of water from three to five minutes, and rinsed somewhat, then it is placed in the above-mentioned developer, which may contain one or two drops more of ammonia than stated above. With a dry plate, an equal flowing over of the developer is of importance, in order to avoid streaks. If the plates incline to form fog, which occurs oftener in high than in low temperature, the addition of bromide of potassium is increased; the same in case of over-exposure. When stronger intensity is desired, take double the quantitity of pyrogallic acid, as stated above, and nine or ten drops of ammonia. The picture develops gradually, and its intensity increases more and more. An addition of one drop of ammonia more helps the development. The ferrous-oxalate developer of Dr. Eder can be used when eight drops bromide of potassium (1:10) to one hundred cubic centimeters developer are added, but it is liable to work hard. Also the prussiate of potash developer
Yellow Prussiate of Potash Solution, 1:4,...........
Pyrogallic Alcohol, 1:10,..............
can be used, but in most cases the pure pyrogallic acid developer is preferable.
The Fixing takes place just as rapidly as the fixing of a collodion plate. The plate is put in a solution of hyposulphite of soda, 1:5. In a few minutes it is fixed. Minute yellow dots, which may, perhaps, remain in it, are nothing but bromide of silver left, which is easily dissolved in continued fixing. After fixing, the film is washed (not longer than a popular candidate for favor, full directions are given below for its use. The advantages claimed by the inventor are its keeping qualities, and the ease with which it can be worked. The plates are coated just as collodion plates are, and may be intensified, fixed, washed, and dried with no more labor. Hence, any photographer may prepare his own plates economically, if the directions in the notes are faithfully adhered to. They are given as received from Dr. Vogel.
collodion plate). It adheres to the plate better than the gelatin emulsion. Treatment with alum is unnecessary.
Intensifying is necessary only in exceptional cases. The following mixture is used for it:
Solution of Iodide of Potassium, 1:10, ...............
5 c. c.
Solution of Bichloride of Mercury, 1:50,..............
This solution is poured upon the fixed and carefully washed plate until the surface of the same shows a distinct greenish-gray color. Afterwards rinse carefully with water. Other intensifiers, even the silver intensifier, may be used with these plates, but the iodide of mercury intensifier is the best; care has to be taken not to let it act too long. The action continues even during the washing. Less rapid, but surer, works Edwards' intensifier, as follows: a Chloride of Mercury, 1: 50.
6 Iodide of Potassium, 1:10.
c Fixing Soda, 1:8.
And twenty cubic centimeters a are mixed with six and a half cubic centimeters b, and six and a half cubic centimeters c. This intensifier can be used also upon the imperfectly washed fixed plate without danger.
Drying and Varnishing. - The plates dry spontaneously in a few minutes; the varnishing is the same as with a collodion plate. A previous coating with gum and similar substances is only to be used when the glass plates have not been coated with caoutchouc, but are gelatinized.
The Re-emfloyment of the Drainings. - The emulsion drained from the plate can be used again after having been filtered. Dilute with one-tenth of its volume of a mixture of three-fourths alcohol with one-fourth acetic acid, and filter warm, either through shirting - which has previously been boiled several times in water, in order to get rid of the starch, and dried again - or through a funnel, in the neck of which clean cotton is placed. The latter is rammed tight with a glass rod, which is left sticking in the funnel. Then moisten with the above-mentioned alcohol and acetic acid mixture, and pour on the drainings. By pressure with the glass rod, the filtering can be regulated.
Cautionary Rules. - "Water precipitates the emulsion, therefore care must be taken to avoid letting drops of water get on the plate which is to be prepared. The vessels for measuring and keeping the emulsion must be perfectly dry. Upon old caoutchouc coatings the emulsion does not adhere as tightly as upon fresh ones. The gelatin coating, however, can be used after months, if it is protected against dust. The rough margins of the plate have to be cleaned thoroughly.