Bromide of ammonium.
Nitric acid.
Alum (powdered).
Hyposulphite of soda (usually called hypo).
The following solutions are prepared from these : No. 1.—STOCK SOLUTION.
Pyrogallic acid 1 ounce.
Bromide of ammonium . . COO grains.
Nitric acid . . . 20 drops.
Water, up to C ounces. No. 2.
Strongest liquor ammonia (•880) . 3 drachms.
Water . 1 pint.
(This will keep some time if well stoppered.) No. 3.
No. 1 . 1 ounce.
Water .. 19 ounces.
• • These are the developing solutions. They should be accurately prepared by weighing and measuring. Guess work will not do.
To prepare No. 1 the twenty drops of nitric acid are added to four ounces of water. This is poured over the pyrogallic acid and bromide of ammonia, and the quan tity is then made up to six ounces. This solution will keep for a considerable time, certainly for some months.
No special precautions are necessary in mixing No. 2. It will keep as long as the bottle is kept quite securely stoppered.
No. 3 will keep for only a few hours, and is made by diluting No. 1 just before development is to he performed.
To save the amateur time and trouble we prepare bottles of developing solution ready for use.
Besides these solutions the following are required :— These latter solutions are best made by pouring warm water over the chemicals mentioned, and stirring till complete solution takes place. They may be used when ever they are cool, and will keep indefinitely. There is no necessity to be with them so exact as regards quan tities as in the case of the developing solutions.
The only apparatus necessary is the following : A measuring glass to hold four or five ounces, and one to hold an ounce.
Three fiat dishes of such a size as to hold the plates to be developed. These are best made of vulcanite or papier-mach6 for the sake of lightness, and to prevent the breakage which is likely to take place if porcelain dishes be used. We here illustrate a flat or developing dish When we are about to commence operations we take the three dishes and place them in a row along the front edge of the operating table. One dish is opposite the -red light, the others are to the right of this one. Space is left between the dish opposite the light and the next one for the glass measure. The bottles containing the developing solutions may go beside the light, so that we may easily place a hand on them in the comparative obscurity in which we are about to work.
Into the middle dish we pour alum solution to a depth of about quarter of an inch. Into the right-hand dish we pour a similar quantity of fixing solution.
The dark slide being placed in readiness in any handy position on the table, we pour into the measure an ounce or an ounce and a quarter of developing solution No. 2, and a similar quantity of No. 3.
All light, except the ruby lamp, is now shut out or extinguished. The plate which was exposed first, and which received the shortest exposure, is removed from the dark slide and is carefully placed, film side upwards, on the bottom of the left-hand dish, which is the only one that is empty. The dish is now taken in the left hand and the measuring glass in the right. The edge of the glass is lowered to the edge of the dish, and the develop ing solution is rapidly tipped on to the plate, a quick rocking motion being given to the dish to make it cover at almost the same instant the whole of the film. All splashing must be avoided, so as to have as few bubbles formed as possible.
The dish is now gently rocked, so as to keep the solution in motion, and the result is closely watched.
After a time, which may vary from five seconds to half a minute, a change will be seen to take place on the surface of the plate, which at first was quite white. Certain portions will be seen to darken. These are the high lights of the picture. To return to our example, the whitewashed wall or line of white clothes : next will appear the half-tones, probably the sky appearing first after the white objects just mentioned. Now we can judge whether or not our exposure has been correct. If it has, the whole of the plate will darken more or less, or, as it is said, will be "full of detail," except those parts representing the portions of the landscape which appeared to the eye quite black. These and these only will remain white, or very nearly so. If large portions of the negative remain white, it is a sign that the exposure has been too short. If the whole of the surface blacken, it shows that the exposure has been too long.