Some thirty years ago, when photography was not very widely understood of the common people, we were passing through the usual ordeal at a douane on the German frontier. One luckless tourist had amongst his luggage several boxes of exposed plates; these were ruthlessly opened to the light of day, lest perchance some contraband article might lie concealed between them. The victim protested bitterly about the destruction of his work, and vowed that he would exact heavy compensation from the authorities. The official merely shrugged his shoulders with the remark: "You talk about your pictures; these plates have nothing whatever on them !"

For, when we return once more to the dark room, and examine the plate taken from the camera, it has apparently undergone no change whatever. There is no difference visible between it and the other plates left in the makers' box. An image has been impressed on the creamy surface during the fraction of a second that the rays of sunlight have been admitted, and will remain there for many years if protected carefully from moisture and light. One instant of exposure to daylight will blot it out for ever. No mortal eye will ever see it unless the plate undergoes development in some reagent capable of translating the subsalts into metallic form.

For most of us, development is a process having a charm of its own, an ever-recurring species of romance. We watch our picture, hitherto seen only by the eye of faith, grow gradually from a few faint blurs into full outline and substance. We are conscious of a magical power which has somehow evolved this portrait of our friend, or this study of nature, as it were out of nothing. We can ill spare this source of pleasure; and so, in spite of the fact that many of the advantages once supposed to belong to dish development have been proved to be illusions, the old-fashioned method is likely to die hard.

Composition Of Developers

A developer consists of (1) the reducing agent or developer proper, (2) an accelerator, and (3) a restrainer. The developer itself, being a strong absorbent of oxygen, must, while in solution, be associated with a preservative, usually sulphite of soda, which also serves to prevent stains.

Accelerators

The majority of developers in common use have an alkaline reaction, and the accelerator employed with them is an alkali, such as potassium hydrate, sodium hydrate, sodium carbonate, or ammonia. The purpose of the accelerator is to set up and maintain the chemical and electrolytic action. Chemically, the alkali combines with the bromine or chlorine of the image to form the corresponding bromide or chloride salt. It was formerly supposed that an excess of the alkaline accelerator reduced contrast in an under-exposed plate, and would "force up" the details of the image; better experience proves that the only result is "fog" over the whole surface.

In certain non-alkaline developers sulphite of soda acts as an accelerator; and with ferrous oxalate the accelerator, hyposulphite of soda, is recommended for a different purpose, viz. the removal of the incidentally formed ferrous salts, which would otherwise retard progress in development.

Restrainers

The effect of the restrainer, either a bromide or citric salt, is to increase contrast by restraining the action of the developer; this influence will be most marked in the lower tones, those parts which have been least exposed to the action of light, and it is therefore a partial corrective of the faults of over-exposure. With normal exposures no bromide ought to be necessary, or, at least, very little; and in practice we prefer to keep a 10 per cent. solution in a dropping-bottlc near at hand, ready for addition to the developer when occasion arises.

Process Of Development

All developers do not act in quite the same way, and we will therefore describe as the typical one, "pyro-soda," variations from this type being noted under the heads of the respective developers. Two solutions will be prepared marked A and B. A consists of pyrogallic acid with its preservative, B of the alkaline accelerator.

Into a glass measure pour 1 oz. of A and 1 oz. of B (cautious workers commence with only a half-quantity of B, adding the remainder when the details of the image have appeared). Two oz. of liquid are sufficient for a quarter-plate, in a flat-bottomed dish, and 4 oz. for a half-plate. Do not be niggardly in the use of developer. It is cheap enough if the worker makes up his own solutions.

Lay the plate, film upwards, in the developing dish and pour the solution in a flood over it, so as to ensure it being covered all over at once with as few bubbles as possible. Then rock vigorously backwards and forwards for a few seconds, to remove air-bells. Within about a minute, if the exposure has been correct, the image will begin to appear as a faint discoloration which will be recognisable as the sky in a landscape; or in a portrait the white collar, face, and hands. These high lights go on darkening and become more defined as black patches, and then, still by degrees, the half-tones assume a grey colour, till at last we can recognise all the chief features of the scene, only with the lights reversed. If the plate were to be removed from the developer at this point the image would be so faint as to be of no value whatever; it must remain for a further period, during which, by electrolytic action, the unchanged molecules of silver salts continue to be reduced till the image has penetrated well into the film towards the back.

Under-Exposure

On the other hand, if the image fails to make its appearance, and the full amount of alkali has been added, we must decide that the plate is under-exposed, and therefore not worth troubling about. But if the subject is irreplaceable, and we are content to have a very inferior result rather than none at all, the dish is covered over, say, with a lidless cardboard box of sufficient size to touch the table all round, and so form a thorough protection from light. We may examine at intervals of ten minutes; but if after half an hour a satisfactory image is not well on its way to completion, hope must be abandoned. No means exist of reinforcing a developer to enable it to define detail on an under-exposed plate.