This Department is conducted in the interest of Amateur Photographers, and the Editor will be pleased to answer any question on the subject so far as possible. Correspondents should address Editor Camera Club Department.
PAPERS FOR BEGINNERS, No. 11.
INTENSIFICATION OR REDEVELOPMENT.
A negative which has been overexposed and developed in a normal developer, while perfect in detail, will be thin and without contrast. This is because it is underdeveloped, the chemicals acting too quickly to allow it to gain density. A satisfactory print cannot be made from such a negative, as the film, being so transparent, allows the light to reach all parts of the paper almost at once, and the print when toned is a dull slaty gray.
An overexposed and underdeveloped plate may be redeveloped, and this process is usually called strengthening or intensifying. Solutions come ready prepared for use, but the amateur who wishes can prepare his own.
The bichloride-of-mercury formula is one of the most satisfactory for the young amateur. This is in three solutions, made up and kept in separate bottles, labelled respectively No. 1, No. 2, No. 3. No. 1 is composed of bichloride of mercury, 120 grains; chloride of ammonium, 120 grains; distilled water, 10 ounces. No. 2 is composed of chloride of ammonium, 120 grains; water, 10 ounces. No. 3 is sulphite of sodium crystals, 1 ounce; water, 9 ounces.
Wash the plate for a few minutes, and then place it for ten minutes in a five-per-cent. solution of alum, and wash for half an hour. Place the negative in a glass tray, and flow enough of the solution marked No. 1 to cover it. The negative will turn white, and as soon as it is white, or nearly so, turn off the solution, and flow with No. 2 for one minute. Rinse the plate again, and cover with the solution marked No. 3, and let it remain till the negative has changed to a dark brown or black. Wash for an hour and dry. No. 3 can be returned to the bottle, but the others had better be thrown away after using once.
Another method is to bleach or whiten the plate with a solution of bichloride of mercury, and then treat the plate with a hydrochinon developer. Dissolve a quarter-ounce of bichloride of mercury in 12 ounces of water. Soak the plate for a few minutes in clear water, till the film is thoroughly wet. Place it face up in a glass tray, and turn the mercuric solution over it, till the image first disappears and again becomes visible. Take the plate from the tray and wash away every trace of the mercury. Place it in a developing tray, and cover the plate with a fresh solution of hydrochinon developer. (Any formula will answer.) In a few minutes the negative will come out almost as strong as if it had been properly exposed and developed. Wash thoroughly and dry. If the plate does not need much intensifying, leave it in the mercuric solution just long enough for the surface to whiten.