DEFECTS, FAILURES, AND THEIR REMEDIES.
the beginner has carefully perused the foregoing chapters upon development, and followed out the instructions therein, he will, in all probability, not be long in coming to the conclusion that the apparently simple operation of taking a negative is not quite plain sailing. His path at the very outset will be beset with various difficulties, and it is with the view of enabling him to steer clear of some of these, and to remedy those which are unavoidable, that this chapter has been written. Of one thing the beginner may rest assured, and that is that nine out of ten of the difficulties in which he finds himself will be of his own creation, and not due to any inherent faults in the plates, or apparatus, which he may be using. It is a com mon fault with many amateurs to endeavour to attribute their failures to defects in their plates; but almost invariably it will turn out, upon investigation, that the and not tho article used, is to blame. Speaking from my own experience, it is only just to members of the trade generally to state that I have always found them willing to investigate any genuine complaint which may be sub mitted to them.
Fog.—This is one of the earliest faults, common to all gelatine plates, which the beginner will meet with, and it is due to a variety of causes. The thick, pea-soup-coloured vapour called " fog," all dwellers in London are only too familiar with, but the would-be photographer will probably want to know to what particular condition of things the term is applied when used in a photographic sense. Now, as there are different kinds of photographic " fog," it will be well to briefly describe their characteristics.
General Fog.—This shows itself in a unifcrm degradation or veiling of the entire image, causing a lack of transparency in the shadows. A negative so affected, when examined by transmitted light, appears literally to be enveloped in a fog, and the beginner will experience no difficulty in recognising it. The defect may exist in a greater or less degree, and its effect upon the results will be that negatives so affected will take a long time to print, the prints themselves being characterised by a general flatness and want of vigour. It may be due to excessive over-exposure, or to the manner in which the emulsion has been prepared.
The defect known as chemical fog is one very rarely met with at the present time. It is seldom found except in extremely rapid plates, and is due to error in the prepara tion of the emulsion. As the beginner should not use plates
of the extremely rapid character, in which the defect would be likely to appear, chemical fog need not further be discussed here.
Light Fog is a defect of a totally different nature, and may be caused in a variety of ways. For instance, too-long an exposure in the camera, an unsafe light in the dark-room, a defect in the apparatus, or an overdose of ammonia when developing. When the defect is due to excessive over exposure of the plate there is no cure, as by the time it makes its appearance the mischief is irremediable. When, however, it owes its origin to some defect in the camera, the fact may be ascertained by examining the plate after development. If the margins of the plate, which are covered by the rebate of the dark slide, retain their white appear ance during development, it may be safely concluded that the fault is to be found in the apparatus, and not in the dark-room illumination. If the fault is due to the camera or dark slides, they should be at once returned to the maker to have the defect remedied. Light will often find its way round the lens flange and through the slot in which the Waterhouse diaphragms are placed; sometimes, too, the glue by which the bellows is attached to the camera, cracks and allows light to enter. The safety, or otherwise, of the dark-room illumination may be readily tested by allowing an unexposed plate to lie upon the dark-room table, at the distance from the light at which development is ordinarily carried on, for about six or seven minutes, keeping half of it covered with a book. Tf, upon development, the un covered portion darkens, the light will not be safe, and an additional thickness of orange paper or fabric should be employed. The reader should, however, understand that very few illuminants are perfectly safe if the plates are exposed to their influence for a very long time, but a8 an abundance of light., of a suitable character, is a great convenience to the operator, it is better to use it, taking the precaution to avoid unduly exposing the plate to its action at the outset, either by keeping the developing dish covered with a piece of cardboard, or by commencing de velopment at the back of the room. When the image is fairly out there will be less danger of fogging, and these precautions may be relaxed.