Reduction - Intensification - Mechanical

Sometimes the negative, from causes already mentioned, may not be quite up to printing standard and may require slight modification, either from over-denseness by reduction, or building up from being thin and flat by intensification. These operations may be conducted in daylight.


It may happen, through over-exposure, a negative is produced which takes a long time to print, owing to the density of the deposit. This may be remedied by treatment in a "Howard-Farmer" reducer, which is prepared by adding a ten per cent solution of ferricyanide of potassium, drop by drop, to solution of hyposulphite of soda, one part in five of water (ordinary fixing bath), until the latter assumes a lemon tint. The soaked negative is placed in this and the action carefully watched, taking it out for examination from time to time. As some reduction goes on in the first stages of washing, the negative should be removed just before sufficiently reduced. Thoroughly wash the negative after reduction.

The second reducer to be considered is ammonium persulphate. If a negative be too "Contrasty," that is, gives chalky lights and intense darks, it may be corrected to a certain extent by immersing in a two per cent solution of the persulphate, removing just before completion, and checking the reducing action by immersion in a weak solution of sulphite of soda. Afterwards well wash.


If from under-exposure or insufficient development a negative is obtained that is weak in contrast and gives a hazy-looking print, matters may often be improved by intensification. The mercuric-chloride and ammonia intensifier will be considered first. The negative is soaked in water to soften the gelatine, and then transferred to a solution made of perchloride of mercury, 20 grains; hydrochloric acid, 5 drops; water, 1 ounce. It should be kept in this until the film is bleached through, that is, it will be white front and back. Wash for about a quarter of an hour in several changes of water; then flood it with a weak solution of ammonia (about half drachm or so of strong solution of ammonia •880 to two ounces of water). The dish containing the negative and solution should be gently rocked until the film is thoroughly darkened to a brownish black. Well wash and dry.

A word of caution must be given here. Owing to the intensely poisonous nature of the perchloride of mercury, extreme care must be exercised in its use. It should always be kept strictly out of the way when not wanted. In the case of young and inexperienced workers, this class of intensification should be entrusted to some competent person to perform.

As the second intensifier, the uranium one will be considered. This combination is very useful, but requires care.

Uranium nitrate .... 6 grs. Water ............ 1 oz.

Glacialacetic acid, 20 minims.

Ferricyanide of potass. 12 grs. Water ............ 1 oz.

Use equal parts, mix as required. They do not keep satisfactorily when mixed. The negative must be thoroughly washed, to remove all traces of hypo.

The intensification results by an altering of the colour of the negative from a black to a reddish; from which cause it acquires a greater light-resisting power. After intensification wash the negative slightly: too much washing destroys the effect. One advantage of this method is, if the result is not as desired, it may be brought back to its original condition with a weak ammonia solution, and the operation repeated, after the negative has been soaked in a dilute solution of acetic acid. If the water used for washing be at all alkaline, it will work as the ammonia and weaken the intensifying action. The best results are obtained when the solutions are slightly acid.

Advantage may be taken of this reducing effect of an alkali to bring about local reduction by applying a weak solution of carbonate of soda by means of a pledget of wool to any part of the negative, where desired. The negative should be held face downwards, the solution applied to the part, and then quickly rinsed under the tap.

Mechanical After-Treatment

By Paper

The printing quality of a negative may also be assisted by mechanical means, as coating the back with "matt varnish" or paper (either tracing paper or Papier Mineral) and working upon these with lead pencil. The varnish is applied by pouring a portion on the centre of the glass, then gently tilting the plate to allow the varnish to flow to the edge, and by further tilting conduct it round until the whole surface is covered. The varnish will quickly dry. Ordinary negative varnish to protect the film is applied in the same way over the face of the negative, which must be first slightly but carefully warmed before pouring on the varnish.

The paper is attached to the back of the negative in the following manner. It is cut to the same size, or, if anything, a fraction smaller than the negative. The cut paper is placed in water to soak, and while it is soaking a narrow band, about 1/4 inch wide, of adhesive paste is applied all round the negative on the glass side. The paper is then taken from the water and all the superfluous moisture removed by pressing with a cloth; it is laid upon the glass and dabbed into contact, commencing at the centre and working towards the margins. The paper, when dry, will stretch very tightly upon the glass; it may then be worked upon with lead pencil to strengthen any high-lights, or made transparent by rubbing in a little vaseline to strengthen the shadows.


Retouching on the front of the negative with lead pencil, to strengthen the high-lights or to remove unnecessary dark portions from the print, is sometimes resorted to. This, however, requires a lot of practice and skill to do it successfully. A liquid known as "The Retouching Medium" is applied and gently rubbed in with the soft part of the finger or with a piece of soft silk stretched over the tip of the finger. When it becomes dry the surface will be in a condition to receive the marks from the pencil, which must be hard and have a sharp point. The pencil must be applied with a very light touch, either as crosses or dots with tails like a comma. Small, over-dense portions of the negative may be scraped away by the skilful use of the retouching knife.