After developing, the bath is poured into the stock bottle, and so long as undissolved crystals remain at the bottom of the bottle hot water may be added from time to time to make up the loss occasioned by spilling and waste, thus the stock solution is always a combination of old and freshly-dissolved oxalate, and I have had one large jar of solution thus in very frequent use for over twelve months, a greenish-black encrustation gradually accumulating at the bottom without detriment.
CONCERNING THE HYDROCHLORIC CLEARING OR FIXING BATH.
Little needs to be said as to the Hydrochloric Acid bath into which the prints are passed immediately after development. The purpose of the acid bath is to dissolve out the sensitive salts which have been unaffected by light and which are still light-sensitive, the removal of these making the paper white and clean. Thus the acid bath is both fixing and clearing in its action.
Into the first acid bath the prints will carry a good deal of the oxalate solution in which they have been developed, and it therefore soon becomes very much discoloured, wherefore after a lapse of about five minutes the print should be removed to a second acid bath of the same strength as the first (pure hydrochloric acid 1 part, water 70 parts) and after five or ten minutes into a third.
After the prints (many may be done at the same time) have been in the third acid for five minutes, the bath should be examined, and if it is quite colourless, that is if the prints have not discoloured it at all, we may rest satisfied that clearing and fixation are complete, but if not, yet another acid bath should be given.
Whilst five or ten minutes in each acid bath is long enough, probably no harm to the print itself, yet no good, will follow a longer immersion. There may, however, be a danger of softening or rotting the paper, a danger which is increased should the bath be made stronger in acid.
If a number of prints are being made, or if numerous dishes for acid constitute a difficulty or inconvenience, we may modify procedure as follows:—
Make up the first acid bath to about half the prescribed strength, say hydrochloric acid one part to water 120 to 140 parts. Into this each print may be flung as soon as developed, until the entire batch is thus far finished. In this weak acid bath the prints will take no harm if left for several hours, when an acid bath (one to seventy) of full strength having been prepared, the first weak solution may be poured off and the fresh poured on. In this the prints should be separately turned over, so that each receives thorough treatment, when the second bath may be thrown away and a third substituted. One dish thus serves for the whole series of acid baths.
If adopting this course, it will be safer not to mix sepia and ordinary black prints in the same first acid bath, after which, however, they may be treated altogether.
Sufficient washing to rid the paper of acid is all that is required to complete operations; but acid does not cling to the print as does hypo, moreover, we have not an absorbent gelatine surface to deal with, so that if prints were dealt with individually and washed by hand, probably a few minutes sluicing under a tap would suffice, but in a properly constructed print-washer, or even a large dish, twenty minutes to half-an-hour should be ample. If any doubt is felt, the last washing water may be tested with blue litmus paper.