It cannot be too weak, and, indeed, I take it as a good test of the suitability of its strength, if the developer begin to act in from half-a-minute to a minute. If any earlier signs are visible, the water jug must be handy. Quantity is of less consequence than promptness.
As long as the very slowest progress is being made do not add potash, but when action ceases, about ¼ dram may be added at a time, and in case the developer has had too much of a drenching to check it, then add pyro. also. Do n't be impatient if five, or even ten minutes are occupied in development. Develope blacker than with ammonia, indeed until only the unaffected shades can be seen. If the development be too rapid, especially at first, a loss of half-tones or intermediate shades will result, giving a harsh print showing great contrasts. The same developer can be used half-a dozen times, or more, for all I know. The secret of success lies in full exposure and slow development. If too dense, the negative can be reduced without deterioration. The mode of doing this will be explained later on.
So much for alkaline development, which, in one form or other, is the most favoured method of rendering the latent photographic image visible. We will now describe a totally different system, which is little practised in this country, but is almost universally used on the Continent. It is known as Ferrous Oxalate Development. It has the merit of not staining the fingers, and for this reason it should be a favourite with ladies. It also possesses the advantage of permitting a dozen or more negatives to be developed in the same batch of developer. Its disadvantage lies in the difficulty of increasing or decreasing its power in cases of over or under-exposure. Those who use it, therefore, should be careful to make their exposures right.
Neutral Oxalate of Potash ... 1 lb. Boiling Water... ... ... I quart.
This solution should be mixed in a basin, and should be constantly stirred until all the crystals are dissolved. It may then be set aside to cool. When cold, it is ready for use, and may be bottled off as a stock solution, to be drawn upon when it is desired to develope a few plates. For use, take 2 ounces of this stock solution, and add to it 1 dram of protosulphate of iron in powder. Stir for a minute with a glass rod, and then add a drop or two of your bromide of potash solution. Having washed the plate to be developed in a dish of clean water for a minute, it can be transferred to a dish containing the developer. The action is much slower than in the case of alkaline development; but when once the image makes its appearance, it speedily gains density, and development may be carried on until nearly the whole surface of the plate appears black. The colour of the finished negative is not yellow, like an ammonia de veloped plate, but is black, like one developed with potash. One great advantage in this is, that the after operation of printing is very much shortened.
If a negative has become extremely yellow under ammonia development, or if it be stained by excess of ammonia, a few minutes immersion in the following clearing solution will speedily remedy the defect.
Alum ... ... ... 2 ounces.
Citric Acid . ... ... I ounce.
Water ... ... ... ½ pint.
Extreme yellowness is also a legacy often left by the carbonate of soda developer. This is better remedied by a clearing solution containing iron. The formula is as follows: -
Alum ... ... ... ½ ounce.
Citric Acid ... ... ... ½ ounce.
Sulphate of Iron ... ... 1 ½ ounces.
Water ... ... ... ½ pint.
The decolouring property of this solution is remarkable, and the negative comes from it with a bloom upon it which is a pleasure to behold. The shadows are cleared, and the dark portions of the film are turned to pearly grey.
It has been already pointed out that an under-exposed negative is not worth keeping. An over-exposed one is very often benefitted by the operation known as intensification. This is the formula: -
Mercuric Chloride ... ... 1 ounce.
Sal Ammoniac ... ... 1 ounce.
Water ... ... ... 12 ounces.
This mixture is a deadly poison, and the bottle containing it should be kept in some corner where it is not likely to be meddled with. A negative can be intensified with it long after it has been fixed, washed, and dried. In any case the negative to be treated should be placed in water to which a little alum has been added for some hours previous to the operation.
If any hypo, remains in the film, the mercury will do more harm than good. Having taken this precaution, immerse the negative in a clean dish, pour upon it sufficient of the mercury solution to cover it, and keep the dish gently rocking, until the image is perfectly bleached. This will take place in about two minutes. Now wash the plate most thoroughly under the tap, and put it in a bath of the following, which may be kept like the mercury as a stock solution: -
Soda Sulphite ... ... 1 ounce.
Water ... ... ... 10 ounces.
In this solution the snow-white image will speedily turn black. When the action is complete the negative must have a final rinse under the tap, and we can then examine it. We shall find that the thin image has become dense, and that what before was a mere ghost, although possessing plenty of detail, is now a good printable negative. Still,let us once more remember that intensification is at the best but a makeshift, and that careful exposure in the first instance will give a far better result.
If a negative is so dense that it becomes difficult for the light to penetrate it in the after process of printing, it has probably been over-developed. It can be easily reduced by the following method. Make a saturated solution of the red prussiate of potash. Also make up a fresh bath of fixing solution (hypo.) of the usual strength. Add 10 drops of the former to the latter, and place your negative in the mixture. Reduction will immediately commence. When it ceases, and if the negative should be still too dense, add another 10 drops of the prussiate and commence afresh. Repeat this again and again until the required density is arrived at.
It now only remains to varnish the negative. This should on no account be ommitted if the negative be valued. The varnish forms a protecting film to the negative which keeps out damp and other destructive influences. For this operation we require proper varnish, an empty dry bottle, and a pneumatic holder. Putting a plate on the holder we gently warm it in front of a clear fire. It must be only warm, not hot. Now pour a pool of varnish in the centre of the glass and by tipping the plate urge it to one corner after the other. Pour off the surplus into the dry bottle, rock the plate from side to side, hold it in front of the fire until it gets thoroughly hot, and the operation is complete. The negative is now ready for yielding prints upon paper. A description of the process will form the subject of our next chapter.