Water........ 80 ozs.
C. K. Co. Sulphite of Soda . 16 ozs. No. 8 Acetic Acid (28% pure) 48 ozs. Powdered Alum . . . . 16 ozs.
Dissolve the chemicals in the order named.
We do not say "Dissolve the chemicals in the order named" from force of habit but with very good reason. If the alum is added to the sulphite before adding the acid a precipitate of aluminium sulphite is formed which it is very difficult to again get into solution. Be sure the sulphite is thoroughly dissolved, then add the 28% acid and then the alum.
Some photographers prefer to dissolve the sulphite in half the water and the alum in the other half, but in compounding, the acid must always be added to the sulphite before the alum.
To make the fixing bath, dissolve 16 ounces of hypo in 64 ounces of water and when sure the hypo is thoroughly dissolved, add 8 ounces of the above hardener. If the hypo is not thoroughly dissolved the addition of the hardener is liable to make the bath milky. The bath should be clear, and if not, it is an indication that sulphur has been released, and with sulphur released the solution becomes a bath as well as a fixing bath.
The addition of any acid (with the exception of sulphurous) to plain hypo will release sulphur. Alum will do the same but not in the presence of Acetic Acid and Sulphite of Soda. The alum is the hardening agent, the acetic acid is the clearing agent and arrestor of development, the sulphite of soda in combination with acetic acid is the preservative, so it is readily seen that the one-solution acid fixing bath answers a three-fold purpose.
Prints could be developed, rinsed in a short stop and clearing bath of acetic acid, fixed in plain hypo and hardened in an alum bath, but the acid fixing shortens the operation and does the same thing better.
The chemical action of sulphite of soda and acetic acid in preventing the formation of sulphur is due to the fact that any sulphur which is formed combines with the sulphite to form hypo. In fact, hypo is prepared commercially in this way by boiling together sulphite of soda and sulphur. If sulphur has already been precipitated in the fixing bath, further addition of sulphite of soda will not dissolve it (or re-form it into hypo) as a cold solution of sulphite of soda is only capable of dissolving sulphur which is about to be precipitated and which at this stage is in a very finely divided condition.
FROM AN ARTURA IRIS PRINT
By Clarence Stearns Rochester. Minn.
Practically all the trouble encountered with the acid fixing bath is due to the releasing of sulphur and its consequent action on the print that is being fixed.Impure sulphite of soda, old sulphite or sulphite that has been exposed to the air will contain considerable sulphate, which has no action as a preservative. If such soda is used in making a bath and it becomes milky it is due to a lack of sufficient pure sulphite.
Sulphite of soda oxidizes even more readily in solution than in its dry form, so the hardener should be kept in a bottle tightly corked, and the prepared fixing bath should be poured into a bottle if it is to be used a second time. Oxidation will destroy a bath that has never been used if it is allowed to stand in an open tray for some time.
Heat will also cause sulphur to be released from the hypo even though a bath has been properly prepared, so it is safest to make the fixing bath only for immediate use in hot weather.
It is as important to wash prints thoroughly after fixing as it is to fix them properly. Prints should be kept separated in the wash water to allow the fixing solution to be thoroughly eliminated from the emulsion. If prints lie matted together in warm water they may begin to tone in spots, or if they are removed from the water before the hypo has been entirely eliminated any portion of the print containing hypo may turn brown after the prints have been laid out to dry.
Acetic Acid No. 8 (28% pure) is specified in our formulas because it is the proper strength for the fixing bath and may be procured at any photographic supply house. You may be depending upon your local source of supply for acids, in which case it is just as well to use Glacial Acetic 99% pure, provided it is properly diluted before it is added to your other chemicals. To make a 28% solution add 3 ounces of 99% acid to 8 ounces of water.
This dilution of the glacial acid is important, otherwise an excessive amount of sulphur dioxide gas would be given off from the sulphite even though only an equivalent quantity of strong acid was employed.
Knowing the action of the acid fixing bath and taking proper precautions to prevent sulphuri-zation will ensure permanent prints even in the hottest weather. And with a stock solution of hardener it is certainly very easy to dissolve sixteen ounces of hypo in sixty-four ounces of water and add eight ounces of the hardener. There is really no excuse for fixing bath troubles either in summer or winter if we will familiarize ourselves with the above facts and keep the precautions constantly in mind.
FROM AN ARTURA IRIS PRINT
By Clarence Stearns Rochester, Minn.