With all gold toning baths the rule is that the gold solution shall be added to the other constituents last of all. If this is neglected with the sulphocyanide bath, you may possibly realise that the rule is dictated by a real need, for under such circumstances it is very likely that the red colouration first formed will refuse to disperse, and then the only possible procedure is to throw the stuff away (which is wasteful) and make up fresh. The peculiarity is that this does not always happen. The bath will sometimes clear, but more frequently not. If sulphite is used as a constituent of the bath, it should be freshly mixed. Old solutions of sulphite are useless for this purpose. It is a debatable point whether the presence of sulphite is an advantage or not. I cannot myself say that I see any great gain in it, but many workers find a decreased tendency towards double tones when using it. I must admit it has not the slightest disadvantage attached to its use, so probably it is wisest to include it. Don't overstep the mark, however : an excess of sulphite will stop toning action almost entirely.
Sulphocyanide (among other objections) has an unpleasant tendency towards softening the gelatine of the paper, and very often leads to frayed edges. These are extremely annoying when prints have been trimmed before toning. Some makers recommend an alum bath before toning, in order to counteract this. I do not like the idea at all, and find it a frequent cause of unequal toning. A weak formaline bath is far preferable, because it has no detrimental action on toning. In fact, I personally add the formaline to the toning bath itself, using about three drops of formaline to every ounce of bath. But as a matter of fact the correct way to prevent frayed edges is to handle prints carefully, never touching the edges at all—never really taking hold of a print at any time, but allowing it to lie on the fingers or on the palm of the hand.
When working a sulphocyanide bath it is needful that all prints intended to be toned in the bath should be inserted in very rapid succession, or else dropped in in a pile and very quickly separated. If one or two prints are put in and allowed to get a fair start before introducing others (which would be a very comfortable way of working if practicable), the first few prints seem to attract all the gold to themselves, and the later prints will suffer from pink half-tones, double tones, and other signs of an exhausted gold bath. The only practical way of working seems to be about as follows :—Sufficient bath is prepared for the batch of prints. This batch will vary in size with the skill of the worker. Twenty is enough for a beginner and fifty a comfortable number for one more advanced. The bulk of the bath must be adjusted with the idea of having sufficient solution for the prints to be separated at all times by a layer of solution. They must not lie close together. This need not entail the use of more gold. Within reasonable limits dilution of the bath will only increase the length of time needed to reach a given colour stage. A very safe strength is one grain of gold (with proportionate amounts of other salts) to fifteen or twenty ounces of water, or two doses of " tabloids" in the same quantity of water. This quantity of bath will point to the use of a largish dish for toning, and it is a very good practice. No toning dish should be smaller than i o x 8, however small the prints may be. Anything smaller than this does not allow sufficient room for the constant movement and changing position of the prints. Having made up the bath, the prints are lifted out of the wash-water in one loose pile. They should not be drained at all, or else they will begin to lie closely together, and toning will start from the edge instead of being equal all over. The whole pile is dropped into the toning bath and quickly swirled around with the left hand first one way and then the other (face down of course). Meanwhile, the right hand is constantly bringing small lots up from the bottom of the pile to be separated by the left hand. After a few minutes of quick manipulation in this way, one can take it a little easier, and bring the prints up singly, quickly examining each one for change in colour. As the desired colour (on the surface) is reached, the prints are thrown into a dish of running water to await fixing.
All toning operations should be conducted by gaslight. If daylight is used, it must be very dim for fear of fogging the prints, and then it is very difficult to judge changes of colour. I find much greater certainty in judging colour by gaslight.
The phosphate bath is a very good one, and, although not suitable for every make of P.O.P., will be found admirable for Barnet papers. It is an extremely quick-acting bath and the prints need careful watching and quick attention. It is not so liable to give double tones as sulphocyanide. The tabloid phosphate preparations give a bath identical in composition to that recommended with Barnet papers, if the quantity of water mentioned in the tabloid instructions is doubled. This is a more convenient strength in use, as the stronger bath is much too quick acting for more than three or four prints at a time. The method of manipulating the prints is the same with this and other baths as with the sulphocyanide, with one possible exception. Mr. H. W. Bennett, when lecturing before the R.P.S. recently, pointed out that if the phosphate or formate baths are made up with distilled water in place of ordinary tap water, there would cease to be any necessity for all prints to go into the toning bath at one time, and they can be inserted one or two at a time. No doubt he is correct, but I always forget to try it because I am so used to the other way, as with sulphocyanide, that I do it from force of habit.
The formate bath is a great favourite with those who have had any long experience with it. The little peculiarities of different toning compounds do not show themselves at first. Like other good things, a toning bath " wants knowing" to fully appreciate its good qualities. One decided advantage of formate over sulphocyanide is the effect on the gelatine of the emulsion. So far from softening it at all, there is even a tendency to harden it, and prints can be handled in a much less respectful manner than in a sulphocyanide bath. A good formula is :—
Soda formate . . . . r5 grains Soda carbonate . . . . 2 ,, Gold chloride - . . .1 grain Water......20 to 40 ounces according to speed desired. Soda formate is not an easy salt to obtain, but is readily procurable in tabloid form. Two tabloids, each of formate compound and gold chloride, dissolved in 20 to 40 ounces of water will give a bath practically the same as the above. At full strength it is extremely quick acting, almost too quick in fact, and the weaker bath will be found far more comfortable to use. Mr. Bennett's remarks re distilled water seem to have special application to this bath.
Gold chloride in combination with soda bicarbonate, soda tungstate, borax, and even washing soda, have their advocates, but there would not seem to be any special advantages over those combinations already mentioned. Soda acetate appears to be somewhat unsuitable for gelatine P.O.P. unless used together with sulphocyanide, and in that case one might as well use the plain sulphocyanide bath.
For matt papers platinum toning will yield an excellent scale of pure brown tones without any suggestion of purple. In this bath prints do not assume the colour they will eventually dry. They tone through stages of claret colour to a violet purple, and a little experience is needed to know exactly when to stop toning. A rich claret colour on leaving the toning bath will dry up a good sepia, whilst if toning is pushed to the violet stage a very rich dark brown results.
Prints intended for platinum toning should, as already indicated, be very strongly printed, as considerable reduction occurs. As they leave the platinum bath the prints should be placed directly into an alakaline bath for a quarter of an hour before fixing. This alkaline solution is conveniently made up by dissolving a tablespoonful of washing soda in a pint of water. Formula for platinum bath :—
Citric acid......20 grains.
Table salt......20 grains.
Potassium chloroplatinite . . 2 ,, or tabloids according to directions.