ALUM-HYPO TONING A method of toning black-and-white prints on bromide and gaslight papers to a sepia colour, sometimes referred to as the " boiling process " and as "sulphur toning" ; actually it is a sulphur toning process, but not the only one. The formula for the bath is : Sodium hyposulphite 2+ oz. 125 g.
Powdered alum . f „ 25 „ Granulated sugar . „ ), Boiling water to . 20 „ r,000 ccs.
Dissolve the " hypo " in the water first, add the alum slowly, and next the sugar, although this may be omitted if desired. When all is dissolved the solution should be milk white and a sediment should form at the bottom of the bottle, but it should not be filtered. The bath should be heated two or three times to about I zo° F. (nearly 49° C.), allowing to cool in between ; this " ripening " is necessary because were it omitted the newly-made bath would not work well, and would bleach the prints. The older and more used the bath is (it may be used over and over again) the more evenly it works, and the richer the tones. When possible, one part of an old bath should be added to four parts of the new bath. Another method of ripening the bath is to tear up some old prints and place in the solution previous to heating ; still another is to add 5 grs. of silver nitrate to each ounce of the bath, this tending to give a purplish-brown tone. The fixed black-and-white prints to be toned should be placed in the bath when this is cold, and the whole then warmed, keeping the prints on the move. The time of toning will vary according to the kind of paper and developer, age of print, and temperature of solution. The quickest results are obtained by raising the temperature as high as the picture will staud, generally about ioo° F. (nearly 38° C.), but the
best tones are those obtained at about 85° F. (between 29° and 3o° C.), the average time being fifteen minutes. The bath may be used cold, in which case toning may take as long as two or three days. Prints developed with amidol appear to tone the quickest, and those toned with hydroquinone the slowest. When the prints reach the desired tone they are allowed to remain in the solution until it is tepid, or cold, and then well washed.
Another method of toning with this bath is to harden the prints first of all in a solution of alum (alum I oz. ; water 3o oz.), or a portion of the cold toning bath, and then place in the alum hypo bath made hot, and, after toning, in the alum-and-water solution again, finally washing. The object of the alum baths is to prevent blisters, which would in all probability occur if the prints were put direct into the hot toning bath, and thence into cold water for washing. The use of the extra alum baths is obviated by warming the toner containing the prints. Rich and good tones depend upon the print having been properly developed, and upon the ripeness of the bath. If the toned prints are washed for about one hour they may be considered quite permanent, the image consisting of silver sul phide.
The alum-hypo bath may also be used for toning P.O.P. prints. The prints must first be washed, fixed in an ordinary " hypo " bath, next placed in a cold alum-hypo bath, where they tone to a good purple-brown colour, and then washed well. P.O.P. prints to undergo this treatment should be over-printed, since they reduce con siderably in toning.