THE INTENSIFICATION, REDUCTION, AND VARNISHING OF THE NEGATIVE.
beginner will find, after he has exposed a few plates, that ono of his greatest difficulties will be to produce with certainty just the requisite amount of density to give a good print. Some of his negatives will be much too dense, while others will be far too thin. At first he will probably not be able to determine, by a mere inspection of the negative after development, whether it is of a character to give a good print or not ; but upon taking a trial print he will find that in some cases he can only succeed in getting a flat muddy-looking picture without contrast, or vigour, and that in others the negatives take an abnormally long time to print, and the results, when attained, are hard and crude. The first of these defects is due to over-exposure, the employment of too vigorous a developer, or one contain ing too little pyro.; and the second to under-exposure, or too prolonged development, or to both combined. Of course, the best thing to do in such cases, when it is prac ticable, is to make a fresh negative by exposing another plate on the subject, modifying the exposure in the direc tion indicated by the result obtained in the first instance. But there are many occasions when it is impossible to do this, and when, at the same time, it is very desirable to get as good a result from the defective negative as it is possible to obtain. Now, fortunately for the photographer, there are two processes by which negatives possessing either of the a,bove-naraed faults may be to some extent improved, and these are called " Intensification " and "Reduction." The meaning of the two terms is probably sufficiently obvious without further explanation. The first one with which I shall deal—namely, Intensification—is applied to a process by means of which the density or opacity of the negative is increased or strengthened, when from any cause it is too thin to give a good print. The second term, Reducing, is applied to the converse process, namely, that of reducing or lowering the density of a negative when it is excessive. It will be readily under stood that these two processes, when intelligently employed, place a wonderful power in the hands of a photographer. But, notwithstanding, my earnest advice to the beginner is to aim at producing, by careful exposure and development alone, a perfect printing negative requiring no after treat ment, and he should always try to avoid the necessity of resorting to either process. However, as I have said, it sometimes happens that partial failure will occur, and then it is that the processes of intensification and reduction stand us in good stead.
There are many formulie given in text-books for com pounding intensifiers, but I do not intend to discuss their relative merits here, nor do I wish to depart from the broad system which I have endeavoured to carry out in writing this book, of presenting one practical and well-tried mode of working to the reader, rather than confuse him by describing alternative methods.
The particular intensifier which I shall advise the reader to adopt is that known as the Mercury Intensifier, and it has the advantage of being 0110 of the oldest methods which have been applied to the intensification of gelatine plates. It is true that it has had one fault alleged against it, namely, that negatives which have been so treated have been found to be wanting in permanence, and have some times become discoloured; but investigation has pretty con clusively proved that where this has occurred the negatives ha,ve not been properly washed between the different opera tions. Undoubtedly, when such precautions are neglected
fading will probably result. The process is an extremely simple one, and the necessary preparations very few. To begin with, the negative which is to be intensified must in the first place have been tlwroughly washed, in order to remove the least trace of fixing solution which might other wise remain in the film. About two hours' washing in running water in the washing tank which has been de scribed will probably be sufficient to effect this. If, as will probably be the case, the negative has been allowed to dry, it must first of all be soaked in clean water until the film has become thoroughly wet. It should then be placed in the dish which has been reserved for the special purpose of intensifying, and some of the intensifying solution, which has already been prepared, poured over it. It will be under stood that the whole of these operations can be performed in actinic light, and, therefore, the change which the plate will now undergo will be clearly seen. It will very soon lose its dark appearance, and gradually assume a white or pinkish colour. This will be more easily observed if the dish in which the operation is performed be a black one. In from three to four minutes the action will probably have proceeded sufficiently far ; the solution may, therefore, be carefully poured back into its bottle, as it will last a long time and may be used over an over again. The caution as to its poisonous nature, which has previously been given, should be remembered, and due care taken not to spill or drop any about the table or floor. The negative must then be most thoroughly washed, for upon the effectiveness of this operation the permanence of the negative will in a great measure &Tend. It should have at least half an hour's washing in running water. At the end of that time it is replaced in the tray, and a weak solution of ammonia (made by adding 15 minims of a 10 per cent. solution of ammonia to 2 oz. of water) poured over the plate. Under its influence the white colour will disappear, and the plate will rapidly darken, ultimately becoming quite black. At this stage the action will have gone sufficiently far, and the plate may be removed from the solution and thoroughly washed under the tap. Upon examining it by transmitted light it will be found to have acquired a considerable accession of density, and will probably be capable of giving a good print. After a thorough washing the operation will be complete, and it may be placed in the rack to dry. The degree of density attained may to some extent be varied by the length of time the plate is allowed to remain in the mercury solution, and by altering the strength of the ammonia bath. If only a slight increase of density is desired, only a few drops of the ammonia solution need be used if, on the other hand, the negative is very thin and requires considerable strengthen ing, the proportion of ammonia may be very considerably increased. Various other alkaline solutions may be em ployed to effect the blackening of the image after bleaching, some photographers preferring to use a few drachms of a saturated solution of sulphite of soda, and where only a little extra density is needed this is to be preferred. In the converse case of a negative requiring a considerable accession of density, equal portions of the two solutions used for com pounding the hydroquinone developer may be mixed and applied to the plate after bleaching.