At least four trays will be required, three being for solutions and one for rinsing. Each tray should be at least 33 inches square inside, by about 6 inches in depth. These trays may be made of wood throughout, with dove-tailed sides, and tongued and grooved bottom, or the bottom may be made of glass. If the work of dove-tailing seems too difficult, the sides and bottom need only be nailed or screwed together, but in this case a lining of waterproof fabric should be fixed to the wood. Trays of this type are inexpensive, and are quite as good as those of a more elaborate character. In some developing works lead-lined trays are used, but they are weighty and cumbersome to handle. In order to draw off the solution when necessary it is well to fit a drain and plug in the bottom of the tray by which the contents can escape into the storage vessel placed beneath the bench.
Sometimes a vertical tank is used. This system is maintained to be the most satisfactory as it enables the solution to be kept more easily in movement. The tank, in this case, should be 33 inches high by 33 inches wide, and 6 inches from front to back. These are inside measurements. It must be lined with waterproof material or with thin sheet lead in the same manner as the tray. For the purposes of the small worker, the tank process is more expensive, owing to the greater quantity of solution that it requires; so, for ordinary and limited working, the tray is recommended. It should be fitted with a rocker so as to enable the solution to be kept flowing evenly over the surface of the film.
The film is mounted upon a special frame. A frame made of wood is most generally used. This likewise a handy man can make at home, although it is not expensive to buy. The middle of each side of the frame is fitted with a short pin to serve as a spindle and to facilitate spinning round when the frame is mounted upon its stand. Each transverse end is provided with guide pins for winding the film.
The other type is known as the pin frame. Its design may be gathered from [Fig. 2]. It is a light skeleton frame with vertical pins projecting from the four diagonal members. The spool is slipped on the central spindle and the film is unwound and passed round the pin on one diagonal, then to the relative pins on the three other members. It is then taken round the second pin on the first diagonal, followed round the relative pins on the other three members, and so on until the whole film has been uncoiled, the pins on the other four cross members being called into requisition as additional supports when the frame is about half covered. When the film is mounted upon this frame it is in the form of an endless square spiral. When the frame is laid in the bath of solution the film stands edgewise. The wooden frame, however, is now almost exclusively used, as it is easier and simpler to work. The film can be transferred to it in a shorter space of time, and the frame with the film upon it can be handled more safely.
The ruby light may be either electricity, gas, or oil, but extreme care must be taken to make absolutely certain that the light is non-actinic, and is not too powerful, otherwise the film, which is extremely sensitive, will be fogged during development. The safety of the light may be tested in a very simple and easy manner. Cut off about 6 inches of film from the unexposed reel, lay it flat upon the developing bench, emulsion side uppermost, in full view of the ruby light. Place two or three coins upon the emulsion and leave them there for a few minutes. Then develop the strip in a covered dish. If the space surrounding the places where the coins were laid comes up grey, then it shows that the light is unsafe, because the exposed emulsion surrounding the coins has become fogged. On the other hand, if no signs of the position of the coins are revealed upon the developed strip, the light is perfectly safe.
The trays should be placed side by side along the bench. The one which is used for developing should stand furthest from the ruby light. If space will allow, the rinsing bath should be placed next to it, but if this is impossible the fixing bath may be placed there. A division board should be set up between the two trays, rising some 10 or 12 inches above their upper edges. This will prevent the fixing solution splashing into the developing bath and spoiling it. Various formulæ have been prepared for development, each of which has certain advantages. As may be supposed, each firm has evolved a formula which it has found from experience to give the best results. Obviously these formulæ are secret. But the most satisfactory for the beginner is that advocated by the Eastman Company. It possesses the advantage of having been prepared by the chemists who are responsible for the emulsion, who understand its particular characteristics and also its limitations. The majority of other formulæ are based more or less upon this one, which is applicable and adaptable to all kinds of work. It has the quality of bringing the picture out to the utmost degree, and by its means many of the errors in exposure may be corrected during development.
The developing solution is made up as follows:—
| Avoirdupois. | Metric. | |
| Sodium sulphite (des.) | 53 oz. | 1,575 grammes |
| Sodium carbonate (") | 25 " | 750 " |
| Metol | 180 grains | 12 " |
| Hydrochinon (hydroquinone) | 8 oz. | 237 " |
| Potassium bromide | 1 oz. 63 grains | 34 " |
| Citric acid | 400 grains | 27·5 " |
| Potassium metabisulphite | 2 oz. | 60 " |
| Water (Imperial measure)} | 8⅓ gallons | 40 litres |
| " (United States " )} | 10 " |