Bromide Papers. - Almost any developer may be used, but one of the most satisfactory is amidol. A stock solution of sodium sulphite is made of about 10 grains to the ounce of water, and a little time before required, 1 grain of amidol is added to each ounce of solution. The amidol need not be weighed each time, but may be measured with sufficient accuracy with a small spoon or on the point of a knife.
N.B. - The sulphite should not be kept more than a few days, as it deteriorates. No bromide of potassium should be needed to prevent fog, so that this developer is very simple and it gives the finest blacks.
Notwithstanding the fact that several prints may be developed in succession in the same developer, it is a rather doubtful policy, as the action soon slows down and there is a tendency to discoloration as the developer becomes weakened.
The time taken to obtain full development will vary with the speed of the paper, the general rule being that the more rapid the paper the slower will be the development. Three or four minutes will probably be sufficient for the one that develops most slowly.
Gaslight Papers. - These differ from the ordinary bromide papers, and always require some bromide of potassium in the developer. The metol-quinol developer has taken the first place, and full directions are given in the packets. When used of full strength the developer may be applied with a brush, the print to be developed being placed on the back of a dish. The image flashes up almost instantly, and development is completed in less than half a minute.
It is very important that no more bromide of potassium be added to the developer than is absolutely necessary, otherwise the tone of the black will be affected.
We will now consider the practical working. In the first instance three papers will be sufficient, and these will readily give all the necessary general knowledge of the process of bromide printing.
1. Rapid White, Smooth Bromide Paper.
2. Slow do. do. do.
3. Matte White Gaslight Paper.
We will presume that 1/4-plate negatives are to be used, and the paper obtained of that size. Prepare, say, 1/2 oz. of sulphite of soda dissolved in 20 ozs. water. Amidol for the bromide paper.
M.Q. cartridges for the gaslight paper and 1 per cent, bromide of potassium.
Now select a negative (preferably a landscape with well-denned clouds and somewhat heavy shadows in the deepest parts) which as nearly as possible answers to what is considered the meaning of a thin negative (Table 3), taking care that it has had sufficient exposure to be full of detail.
Examine it carefully in a good light, and notice the most dense portions that show some sign of detail. If any cloud is shown in any part of the sky then take that portion for the purpose of obtaining the correct exposure as described below. If there is not any cloud, then notice particularly any portion of the distance which is but little less dense than the sky.
The object is to find as previously noticed, some portion of the picture which should be just represented in the print by a very faint tint, and then to find the amount of exposure to the light that will just give this result upon full development. This is the exact opposite of the good old rule in negative making, " Expose for the shadows and let the high-lights take care of themselves." That which cannot be done in the negative is possible in bromide printing, so that the rule may stand. Expose for the high-lights, and if the shadows don't come right of themselves, a slight extra treatment will probably bring them right.
We will presume that the source of light chosen is a No. 5 Bray gas burner, and having in the dark-room placed, say, one quarter of a sheet of slow bromide paper upon the selected portion of the negative in an ordinary printing frame, we will give a trial exposure of 20 seconds at the point 4 on the scale, equal to 80 seconds at 1 on the metre scale. If the area of the trial portion will permit of being divided up, time will be saved by obtaining three exposures on the same piece of paper, thus : - Cover the front of the frame with a card, and when the frame is in position before the burner, uncover one-third of the paper for 20 seconds, then another third for 10 seconds, and remove the card altogether for 10 seconds more. The exposures will then have been 40, 20 and 10 seconds respectively, equal to 160, 80 and 40 G.M.S. at point 1. If, after full development, by which is meant that fresh detail no longer continues to appear, the desired exposure is not found within this scale, but evidently greater or less, a guide will have been obtained for a second trial.
We will suppose that the portion that has had 20 seconds appears a little too dark, and that with 10 seconds does not show at all, but is quite white ; then it is evident that an exposure of about 15 seconds or 60 G.M.S. should give at any rate this one portion of the picture as desired.
We may now proceed to make a full-sized print from the negative, and see what knowledge can be gained from the result obtained.
There is one thing that should be constantly borne in mind - the finished dry print is always less brilliant than when wet, so that the exact final appearance cannot be ascertained until it is dry. After a few trials it will be comparatively easy to estimate this difference and to learn when a wet print is satisfactory.
Having, then, obtained a print exposed 15 seconds at 4, developed, fixed, washed and dried as directed in the instructions with the paper, we shall find that the high-lights are very closely correct, but the shadows may not be satisfactory. In any case whatever, the following table will be found to cover all points and show both cause of difference and remedy.
1. Very black shadows. Too brilliant result.
Negative too much developed for the paper used ; gradation of paper insufficient.
Try again with more rapid paper (if rapid paper had been used the modified treatment to be described would be required).
2. Shadows good.
3. Insufficient depth in shadows, flat result.
Negative not sufficiently developed for the paper used, gradation of paper too great.
Try again with a slower paper.
It will be noticed that no such table as this could be made unless full development were the rule in working, and the remedy might not then be easily found because of the complication of causes of error.
As it will now perhaps be necessary to try working with the gaslight paper, the only points to be observed are : 1. The usual dark-room is not needed, but it may be lighted with an ordinary gas burner.
2. A developer containing bromide of potassium must be used, as described in the directions.
3. The exposure may be to the gaslight as before, but requires so much time that it is more readily made by burning magnesium ribbon. One inch lighted at the distance marked 8 on the scale would probably be suitable for a first trial. The rest of the work will follow in the same manner as described for bromide paper.