802. Acid Chrome-Alum Fixing Bath

Acid Chrome-Alum Fixing Bath. This kind of a bath has been in use for years and is preferred by many (mix only in the order given) :

803. Acid-Fixing Bath. (For Lantern Slides.) - An acid-fixing bath for lantern slides is made as follows (chemicals must be mixed in order given only):

Sulphite of soda, 1/4 ounce; dissolved in 1 ounce of water, and then add 30 drops of hydrochloric acid. Stir well. In a separate vessel, dissolve:

Hypo-sulphite of soda, 4 ounces, in 20 ounces of water. When the hypo is all dissolved, add the acidulated sulphite solution to the solution of hypo. (Not the reverse.) The whole being gently stirred during the mixing.

804. Alum - Alum is frequently employed for the purpose of hardening the film, especially in hot weather, but its use is attended with considerable danger to the negatives, as alum and hypo mutually decompose each other with the production of new substances, which endangers the natural life of the negative. If used as given in our acid chrome-alum fixing bath it is all right.

805. Formaline

Formaline. Formaline, or Formaldehyde, is a gas which dissolves to a large extent in water. A solution of the strength of forty percent, is sold commercially. This liquid diluted with from ten (10) to twenty (20) parts of water (1 ounce to 20 ounces), makes a bath which may be used to harden the gelatine film, and is easily washed out and not likely to do any harm. After the plate is developed and then washed for two or three minutes, it is placed in the above mentioned solution (1 to 20) for three or four minutes. The plate should then be rinsed and placed in the hypo bath as usual. After fixing, the film will be found so tough and insoluble that the negative may actually be washed in water hotter than the hand can bear, without any sign of softening. Negatives so treated dry much more quickly than when treated otherwise. Plates slightly washed after fixing may be treated with Formaline (1 to 16)if preferred, and then washed as usual.

806. Washing After Fixing

Washing After Fixing. it is desirable that washing after fixing be quickly and thoroughly done. If running water be available, an hour is long enough; when the water supply is limited, the plate may be washed in a flat dish, frequently rocked, for five minutes or so; the water being then drained off and a fresh quantity added, and the process repeated until the plate has had a half to three-quarters of an hour washing. When left to wash in running water, it is better for the plate to be placed vertically in a grooved box than to lie in a flat dish, thereby avoiding any sediment which is likely to settle on and stick to the soft gelatine surface. When a plate has been sufficiently washed, it is well to hold it (face upward) under the tap of running water and lightly wipe over the surface with a pad of filter cotton, in order to remove any sediment which may have settled on the film from the washing water. To prevent sand or rust from striking the negatives while washing them, tie a piece of cotton flannel over the faucet.

807. Drying the Negatives - Plates are best dried in a moderately warm room, the temperature of which should not vary much, with good ventilation. They should not be placed too close together. A plate must never be laid in the sunlight to dry, as this may melt the film, cause transparent holes, and, if nothing worse, will increase the intensity. In cold weather do not allow the negative to get too cold while drying; this not only retards the drying, but in case the moisture therein should freeze, it will cause mottled spots. If the negative is partly dry and then removed to another room which is much warmer or colder, it will cause a difference in the intensity of the part to dry last. If a negative be wanted in a hurry, it may be quickly dried by laying it for ten minutes {after thoroughly -washing) in a bath of alcohol, then it will dry rapidly. If dried in this way the negative must first be very thoroughly washed, for if any hypo be left in the film, an insoluble white deposit may be formed, which cannot afterwards be removed.

808. Halation - Halation is the spreading of the strong lights of a negative and consequent encroachment upon the shadows. In a view negative including a bright sky it is generally found, on development, that the extreme edge of the plate above the sky, which was protected by the rebate of the dark slide, does not remain clear, although the other three edges may do so, the strong light of the sky having spread beyond its proper boundary. When a picture is taken of the dark interior of a building including a window, the light of the latter often seems to spread and form a wide blur all around. (Can be remedied by local reduction.)

In the ordinary negative the effect of halation is scarcely apparent; but, nevertheless, it is there more or less generally, and is detrimental to the fine details. Halation is due chiefly to light which has passed through the film and been reflected from the back surface of the glass plate. It is also, to a minor extent, caused by a lateral spreading of light from particle to particle of the silver bromide in the film. Some plates are more liable to halation than others; this depending on the opacity and other characteristics of the film. The Hammer Plates, even when not backed, are notably free from it; but the Hammer Aurora Double-Coated (Non-Halation) Plate is prepared especially to prevent halation. We recommend their use, especially for interiors, landscapes and marine views, as well as for groups and white draperies. Expose for the darkest shadows and use a rather dilute developer.

809. We also furnish a backing, "Acme Halation Destroyers," which is a good article for sticking in optical contact with the glass. It helps to overcome the halation effect. We also furnish plates backed with this medium when so ordered.