We will now consider the treatment of a negative which is over-dense, and requires to be reduced. There are several methods by which the process known as reduction may be effected, but I shall only describe one. I may, however, mention, that when only very slight reduction is necessary the negative may be sufficiently reduced by allowing it to remain for a short time in an ordinary clearing bath, com posed of a pint of saturated solution of alum to which half an ounce of hydrochloric acid has been added. When, how ever, the negative is very dense, more vigorous treatment will be necessary. Two ounces of water are poured into a clean measure, and about ten drops of a solution of per chloride of iron (of the strength used in pharmacy) added. The negative, if dry, should have been allowed to soak in water, in the manner already described, and is then placed in a tray, and the solution poured over it, and allowed to remain for a few minutes. It is then removed, but no visible change in its appearance will be detected at this stage. It should then be placed in a second tray con taining three ounces of water, to which has been added about two drachms of the saturated solution of hypo. The reducing action will at once commence, and the plate must be carefully watched, as the action sometimes proceeds so quickly as to be almost beyond control ; in which case over reduction might ensue, and the negative be spoilt. If, on the other hand, the reducing action proceeds very slowly, a few drops more of the solution of perchloride of iron may be added to the first solution, and the negative re-immersed, and, without washing, again re-transferred to the hypo. solution, when probably the action will proceed. These solutions must be thrown away after use, and the dishes, of course, thoroughly washed. When the reduction has pro ceeded sufficiently far, the negative is to be removed from the solution and thoroughly washed.
The beginner should make it a rule to take a trial print from every negative with a view to ascertaining its printing qualities, and whether it requires to be either intensified or reduced; and if it does not, it should at once be varnished.
If, however, either intensification or reduction be necessary, varnishing must be deferred until those operations have been carried out. The object of varnishing is to protect the film, which, though apparently tough, is very liable to become scratched or stained by contact with the silver paper used in printing. Stains so caused are extremely difficult to remove.
The operation of varnishing a negative is very often a difficult one to a beginner, and as it can only be learnt by practice, be will do well to make his first attempts on some spoilt negatives. The object is to cause the varnish to flow over the entire surface of the plate without forming mark ings or ridges which might show in the print. Any good negative varnish may be employed. Personally, I prefer Hubbard's, and always use it. The negative to be varnished should first be lightly brushed with the camel-hair brush to remove any adherent dust, and then held over a gas flame until it is just as hot as the hand can bear. The plate should then be held between the. thumb and finger of the left hand in as nearly a level position as possible, and a pool of varnish poured in the middle ; the plate is then slightly inclined so as to cause the varnish to flow towards and fill up one corner of the plate, and, directly it does so, tilted so that it runs to the next corner, repeating the tilting with a slight rotatory movement until the varnish is made to cover the last corner, when the plate must be tilted vertically, and the excess of varnish allowed to drain back into the bottle. The rotatory motion must be continued at this point in order to avoid the formation of ridges. The plate must then be held over the gas flame or in front of a fire until the varnish sets quite hard, which it will do in a few minutes. The operation, although a difficult one to describe, may easily be acquired with a, little practice. Varnishes are now supplied which may be applied to the plate with a camel-hair brush ; but such a mode of working is very clumsy, and one which I would not recommend the reader to a,dopt. The negative, after varnishing, will be ready to print from.