T. Thorne Baker

If for the term " why and wherefore ", we had substituted the word "chemistry," the beginner would very likely have passed over this article, thinking it altogether beyond his ken. It is not, then, to be chemistry at all, but merely a simple chapter on the reasons for doing as we do in development, and, in order to make it quite seasonable, it shall deal exclusively with the development of lantern plates and bromide and slow contact, or " gaslight papers.

It would be quite possible to lay down a vast series of laws, of what to do in development, what to avoid doing, and what steps to take in various cases, so that an amateur photographer who could bear them all in mind and put them into use would be capable of dealing with any emergency. But if, right from the start of photographic work, the amateur would ask the question, what is he doing, and why, and thus understand a reason for every action, the time would very rapidly come when his own knowledge of the "Why and Wherefore" would enable him to cope with all difficulties without troubling a friend, textbook or all-patient Editor for information.

Development, when considered seriously, is a remarkable thing, and must arouse curiosity in the mind of every photographer at some time or other. It requires little thought, however, to see that the developing solution turns the film of a plate or piece of bromide paper black wherever the light has acted upon it„ i. e., wherever it has "Been " the light.

A piece of P. O. P., if put into some developer, will turn black almost immediately, whether it has " seen" the light or not, and this behavior is characteristic of every brand of printing-out paper which requires the-continued action of daylight to print it to sufficient depth.

A lantern plate is a piece of glass, coated on one-side with a mixture of gelatine and a cream colored substance called silver bromide; the same mixture is used for bromide papers. In some makes other sub-stances are, of course, used as well, but silver bromide will be sufficient for our purpose here. During the exposure of a lantern plate behind a negative, a physical change quite invisible to the eye takes place in every portion of the film where the light is able to reach it; thus the black portions of the negatives or "high lights, " do not allow light to reach the lantern plate-film, while the light can pass freely through the clear portions or "shadows" of the negative, and thereby produce the physical change already referred to. The nature of this change is too complex to be discussed here, and hence only its consequences need interest us.

Suppose that now we place an exposed lantern plate in some developing solution and watch the progress of development. First of all, the developer consists of, let us say, hydroquinone and soda, originally in two solutions, A and B. A consisted of the hydroquinone in water, together with some preservative, such as sodium sulphite, and B of caustic soda in water; in the mixed developer, therefore, we have all these things, and always a little bromide as well.

The change that took place during exposure has made the following difference in the film: Wherever the light got through a clear portion of the negative exposure and reached the plate, the film will begin to turn black, whilst the protected parts will not be in any way altered. If no caustic soda or alkali were present, the development would proceed very slowly; the soda, however, neutralizes, or "kills "this acid, and the more we put in the developer the quicker does it act, and the result is that the dark parts of the image become sufficiently developed before the half tones or delicate portions are of sufficient depth or density. Thus it is necessary to adjust the proportion of soda to hydro-quinone, or carbonate to metol or whatever it may be (in general "alkali" to "reducer"), with precision; hence the necessity for a reliable formula.

A lantern plate or bromide paper developer must contain the following parts: the developer itself, such as hydroquinone; the preservative, such as sodium sulphite; the alkali, such as sodium carbonate; the solvent, water; and, finally, what we may discreetly term the safety-valve, potassium bromide. Our bottle of ten per cent bromide solution is an all-powerful lever; it ensures purity in the whites, it regulates contrast, and is in every way a necessary thing.

Bromide is such an important thing, in fact, that we had better just see how and why it works. A sheet of gaslight paper, unexposed to light, should be left in a metol-hydroquinone developer, and another, sheet in a similar developer, only to which several drops of ten per cent. bromide solution have been added, for the same time - say one minute. On then examining them, it will be found that the piece developed in the presence of the extra bromide is infinitely cleaner or " whiter " than the other. This ex-l)eriment alone teaches us two things: First, that the paper will fog, or turn discolored, even if it has no exposure, on prolonged development; second, that the fog produced by the developer is prevented by bromide, at any rate, to some extent. We are thus taught the following:

1. Never leave a lantern plate or piece of development paper in the developer longer than is necessary.

2. If the whites do not seem pure, add an extra drop or two of bromide solution to the developer.

It also follows from what we have said that too much bromide in the developer will destroy the softest gradation, and give us very clean but very harsh pictures.

That the amount of carbonate or caustic in a developer must be accurately arranged, has already been pointed out, and this is not only because a developer such as hydroquinone requires a specific quantity. but also, since the amount varies very considerably with different developing agents. Amidol, for instance, does not require any alkali at all, and the best formula is made up thus:

Sulphite of soda 10 parts.

Water 100 "

Amidol 1 "

Here, again, the amount of amidol may be varied ; more amidol gives greater density, less gives less, just as if an alkali were present; the bromide, too, must be present, in order to ensure cleanliness.

When development is finished, we have a black image consisting of decomposed bromide of silver resting on, and in, the original creamy white film. It is obvious that this unusedsubstance mustbe removed, and we therefore put the plate or paper into a "fixing " bath which dissolves away any silver bromide not affected by light during the exposure. Remember that the ordinary light should never be turned on in the dark-room, nor the plate removed from the red light until thorough fixing of a lantern plate or rapid bromide paper is accomplished.

As hypo dissolves the white silver salts, it is at once evident how careful we must be not to allow any fixing solution to drop into the developer. The more we know of the action of our various chemicals, the greater need we shall see of cleanliness.-" Amateur Photographer. "