Distorted Films. A film which has been dried too rapidly (in too dry and warm air), under excessive tension, is often waved at the edges. The remedy consists in washing until the gelatine is uniformly swollen, and then drying under normal conditions.
White, Granular Deposit. This deposit, which is quite distinctly rough to the touch, is caused by the deposition of lime salts from a very hard water when no final rinsing in soft water has been employed. It may be removed by washing in slightly acidified water (1 per cent hydrochloric or acetic acid is suitable, but non-volatile acids must not be used) and again drying.' White, Powdery Deposit. This is usually caused by aluminium sulphite deposited in or on the gelatine from an acid-alum fixing bath in which too much of the acid has been neutral ized. It may be removed by a few minutes' immersion in a solution of carbonate of soda (about 10 per cent) followed by washing in clean water.
Yellowish-white Opalescence. This veil is gen erally due to the deposition of sulphur in the gelatine caused by the acidification of a fixing bath containing insufficient sulphite, or by the use of an acid fixing bath at too high a tem perature, or by treating the negative with alum before or after fixation without intermediate rinsing. The only possibility of dissolving this sulphur without affecting the image is, after thoroughly hardening the gelatine, to try to convert it into hyposulphite of soda in a warm solution of sulphite (rip per cent solution of anhydrous sulphite of soda, warmed to about no° F.), in which it is allowed to remain for some minutes. The process is finished by wash ing in several changes of water. The treatment is not successful with old negatives.
Silvery-white Opalescence which is Yellow by Transmitted Light. This variety of white de posit, covering all or part of the image, and particularly parts which have been dried too rapidly (edges), is caused by too rapid dehydra tion of the gelatine by concentrated alcohol (neat methylated spirit), especially if the negative has been washed in very hard water. It may he removed by washing in slightly acidified water (see "White Granular Deposit "), which method may also be employed as a preventive.
436. Defects Occurring in a Negative After Drying. Ink Marks or Stains of Aniline Dyes. Black ink stains (indian ink excepted) or coloured stains arising from dyes or any coloured substance (including dust from a copying pencil) disappear entirely under the treatment described in § 432 for developer stain.
Brown or Black Stain Due to Silver Nitrate. In printing with print-out papers which contain soluble salts of silver, a splash of water on the negative or the paper causes a transference of a little silver nitrate from the paper to the gelatine of the negative. This silver nitrate is gradually reduced under the influence of light, and gives a brown or black mark. This stain is composed of silver in a considerably finer state of division than that of the silver in the image itself, and, as a rule, may be removed, without appreciable weakening of the image, if the negative is treated with one of the weak silver solvents employed for destroying dichroic fog (§ 433).
Brown Stains. Brown stains may appear on a negative after the lapse of time ranging from some weeks to several years (more rapidly in a moist atmosphere). This is due to the slow conversion into silver sulphide of silver hypo sulphite left in the negative after incomplete fixation or washing (in the latter case there is often a general weakening of the image in the region of the stain). There is no certain method of removing this kind of stain it is often better to make a new negative from a print taken before the defect arose, or to make, first, a positive transparency (§ 570) on a panchromatic plate through a deep orange screen, and then a fresh negative from that. The effect of the stain is thus greatly reduced.
Scratches. The effect of various fine markings, produced by friction, may be reduced by varnishing the negative (§ 477).
Cracked Negative. A cracked negative, of which the gelatine film is intact, may be saved by stripping the film to another support (§ 482), provided that the broken glass is at once made good. This may be carried out very simply as follows : Take an old, waste negative, and dip it in water for a very short time, so that the gelatine does not swell appreciably, then slide the back of the cracked negative gently on to the moist gelatine so prepared. The very thin film of water interposed is absorbed by the gelatine and perfect adhesion of the two nega tives is then assured on account of atmospheric pressure.
The Gelatine Film Scales Of or Becomes Powdery. This has frequently been noted with old negatives which have been hardened with formaline.