Should all these devices fail, the plate is hopelessly under-exposed.
Sometimes, when working with a diluted developer as just described, it happens that although all the necessary detail has been brought out, the image gains in opacity very slowly. Provided that all the required detail is visible, small quant.i.ties of pyro solution may be added in order to gain opacity more quickly.
[Ill.u.s.tration: TEASELS By Carine Cadby.]
PYRO-SODA DEVELOPMENT.
When sodium carbonate is used as the alkali in place of ammonia the developer acts somewhat more slowly and is less liable to produce fog, especially with very rapid plates, and there is very little tendency to produce green fog. On the other hand, variations are not so easily made in the composition of the developer. Some people find the absence of the smell of ammonia a decided advantage.
STOCK PYRO SOLUTION.
The same as for Pyro-Ammonia.
DILUTE PYRO SOLUTION.[2]
Stock pyro-solution 1 oz. or 10 parts Water 10 oz. or 100 parts
SODA SOLUTION.
Sodium carbonate, crystallised. 1 oz. or 10 parts Sodium Sulphite 1 oz. or 10 parts Pota.s.sium bromide 10 grains or 0.23 part Water to make up to[3] 10 oz. or 100 parts
[2] No more of the dilute pyro solution should be made up than is likely to be used during the same day, but it will keep well enough for a day or two.
[3] The sodium sulphite and carbonate are dissolved, with the aid of heat, in about 8 oz. (80 parts) of water, the bromide added, and the liquid when cold made up to 10 oz. by adding water.
For use mix equal parts of dilute pyro solution and soda solution and pour over the plate.
If the exposure has been correct the image will begin to appear in about a minute, and development is then allowed to go on with occasional rocking of the dish, until the negative is sufficiently opaque.
If the plate behaves as if it were under-exposed, _at once_ dilute the developer with an equal bulk of water and pour it back over the plate. If the high-lights continue to increase in opacity, but the rest of the image does not appear, add some more of the soda solution with or without some more water. Should parts of the plate still remain blank, apply some of the soda solution to them with the aid of a brush as described under pyro-ammonia (page 32).
If the rapid appearance of the image indicates that the plate is over-exposed, at once pour off the developer into a measure or mixing gla.s.s and rinse the plate well with water. Add to the developer a small quant.i.ty of pota.s.sium bromide solution (1 in 10 of water) which should be kept at hand for this purpose. A small quant.i.ty of pyro stock solution may also be added. The developer is then poured over the plate again. When the over-exposure seems to have been considerable, the amount of pota.s.sium bromide added may amount to 4 grains (or 40 minims of the 1 in 10 solution) per ounce of the developer, but this proportion should not be exceeded; even small quant.i.ties of bromide in the pyro-soda developer have a marked influence in r.e.t.a.r.ding development.
When there is reason to suspect over-exposure, not more than half the soda solution should be added at the beginning of development, and the rest may be added or not, as the case may require.
DEVELOPMENT WITH ORTOL.
ORTOL SOLUTION.
Ortol 130 grains or 1.5 parts Pota.s.sium metabisulphite[4] 65 grains or 0.75 part Water to make up to 20 ounces or 100 parts
SODA SOLUTION.
The same as for pyro-soda.
[4] See foot-note to page 30.
Mix equal parts of ortol solution and soda solution.
This developer behaves in much the same way as pyro-soda and gives very similar results. It has the advantage, however, that it does not stain the fingers, and has practically no tendency to produce either fog or stain on the plates. Moreover the same quant.i.ty of solution can be used for several plates; when the action becomes perceptibly slower or weaker, part of the old solution is poured away and an equal quant.i.ty of freshly mixed ortol and soda solutions is added.
The chief differences to be observed are (1) that the different parts of the image follow one another more rapidly than with pyro-soda, even though the plate may have been correctly exposed, and (2) the colour of the reduced silver is somewhat bluer than with pyro-soda, and therefore in order to obtain the same degree of _printing_ opacity, as distinct from visual opacity, development must be carried a little further.
Apart from these differences, what has been said of pyro-soda holds good for ortol soda and need not be repeated.
DEVELOPMENT WITH HYDROQUINONE (QUINOL).
QUINOL SOLUTION.
Hydroquinone 90 grains or 2 parts Sodium sulphite 1 oz. or 10 parts Water to make up to 10 oz. or 100 parts
ALKALI SOLUTION.
Pota.s.sium carbonate (dry) 1 oz. or 10 parts Pota.s.sium bromide 20 grains or 0.46 parts Water to make up to 10 oz. or 100 parts
Mix two parts of hydroquinone solution with one part of alkali solution and one part of water, or, if a more energetic developer is wanted, mix equal volumes of the hydroquinone and alkali solutions.
Hydroquinone is not an advantageous developer for general purposes, but it is useful when negatives are required showing strong contrast between the highest lights and the deepest shadows, and especially when it is important that there should be no deposit at all in the deepest shadows. This is the case, for example, when copying line engravings, pen and ink drawings and similar subjects.
DEVELOPMENT WITH FERROUS OXALATE.
This method of development also is not well adapted for general work, but it is invaluable for certain purposes. The reduced silver has a pure grey-black colour and there is exceedingly little tendency to produce fog of any kind. On the other hand, the developer admits of little modification in its composition and therefore the exposure must be fairly correct. It is also important to avoid contamination with even minute quant.i.ties of hypo, since this substance very readily causes stains.
FERROUS SULPHATE SOLUTION.
Ferrous sulphate 2-1/2 oz. or 25 parts Sulphuric acid Small quant.i.ty Water to make up to 10 oz. or 100 parts
About three-quarters of the total quant.i.ty of water is mixed with a small quant.i.ty (not more than 50 minims per 10 ozs., or one part per 100) of sulphuric acid, and the ferrous sulphate (proto-sulphate of iron) which must be in clear pale green crystals without any yellowish incrustation, is dissolved in it with the aid of a gentle heat. After the solution has cooled, it is made up to the specified volume with water. This solution alters when exposed to air, and should, therefore, be kept in small (2 oz.) bottles, filled up to the neck and tightly corked.
OXALATE SOLUTION.
Pota.s.sium oxalate 10 oz. or 25 parts Pota.s.sium bromide 40 grains or 0.23 part Water to make up to 40 oz. or 100 parts
For use take four parts of oxalate solution and one part of ferrous sulphate solution, pouring the latter into the former and _not vice versa_. In order to obtain slower action with a rather softer image and a slightly browner deposit, the developer may be diluted with an equal volume of water. Slower action, with slightly increased printing contrasts, and clearer shadows, results from an increase in the proportion of bromide.
FIXING.
After development is finished, the dark-coloured reduced silver that forms the image remains mixed with a considerable quant.i.ty of semi-opaque, yellowish unaltered silver bromide, which would not only interfere with the printing, but would also gradually darken when exposed to light. The negative must therefore be "fixed" by dissolving out the unaltered silver bromide, and this is accomplished by immersing the plate in a fairly strong solution of sodium thiosulphate (formerly called sodium hyposulphite) commonly known as "hypo." The usual strength of the fixing is as follows:
FIXING BATH.
Hypo (sodium thiosulphate) 10 oz. or 25 parts Water to make up to 40 oz. or 100 parts
A solution of double this strength is, however, not unfrequently used, and acts more rapidly, especially in cold weather.
The developed plate, after being well rinsed with water, is placed in the fixing bath and allowed to remain in it with frequent rocking until the silver bromide has all been dissolved out of the film.
This is ascertained by lifting the plate out of the dish and looking at the back by reflected light, the plate being held in front of something dark. It is not difficult to see whether the silver bromide has all disappeared or not, but in order to ensure complete fixing the plate must not be taken out of the bath as soon as this has happened, but should be left in for a few minutes longer, the dish being rocked so that the dissolved silver salt may diffuse out of the film into the fixing bath.
When removed from the fixing bath the plate should be allowed to drain into the bath for a few moments and should then be washed for five or ten minutes in running water under the tap. It is best to put the plate in a dish standing on the sink and have a piece of flexible indiarubber tubing reaching from the tap to within a couple of inches or so of the top of the dish, so that the water may not splash too much. After washing in this way, the plate is placed in a grooved zinc rack, which is immersed in a tank (preferably of zinc), containing sufficient water to completely cover the plates, and here it remains until the whole batch of plates in hand has been developed and they can all receive their final washing together. The plates stand upright in the rack, and the entrance and exit of the water must be so arranged that the water enters at the bottom and overflows at the top, or, what is perhaps better, enters at the top and is drawn off from the bottom, the waste pipe opening at the bottom of the tank and being bent and carried upwards until its mouth is at the level at which the water is to stand in the tank.
When running water is not available the plates may be washed in dishes. After being well rinsed to remove the adhering hypo solution, the plate is covered with water (about 3-1/2 oz. for a half plate or 5 oz. for a whole plate) and allowed to remain with frequent rocking for five or six minutes. The water is then well drained off, a second quant.i.ty added and allowed to remain for the same time as before, with frequent rocking, when it is poured off in its turn. Treatment in this way with six successive quant.i.ties of water will remove all the hypo, provided that the film has not been treated with alum.