Originally Posted by shadowfox
That sounds interesting, do you happen to have a scan of the prints toned this way?
Here are two, toned using the Hypo-Alum hot toning method. These are from about 20 years ago, printed on Chinese made Xiamen chlorobromide paper. The scan and web rendering don't quite show the nuances of the sepia tone:
The Hypo Alum process is quite simple.
The toner formula is practically a Fixer bath which has gone bad:
Sodium Thiosulphate (10 water)- 200 g
Potassium Alum - 40 g
Water QS to 1 litre.
Hot water (60deg C) is used to mix the two ingredients. It will cloud immediately and a sulphuric sludge will form. To season the toner, a bit of silver nitrate (0.5 g) is added. Or the silver reserve can be provided by tossing 3 to 4 sheets of undeveloped 8X10 paper into the brew. The presence of silver is needed to prevent the toner from eating away the silver print image.
The silver sludge must not be removed or filtered out.
To use, the solution is heated to about 50 deg C, and the prints are slid into it. Toning would take about 10 or more minutes. The prints to be toned need not be washed thoroughly since the toning bath is just like the fixing bath. A developing tray placed in a heated water bath will work for this purpose. I used to put enamel metal trays over a hot plate to do this.
Once the prints are toned, they are washed in running water. Wash the usual way needed for prints. The silver sludge that the print may take along can be wiped off. The print will have a hardened emulsion as well. The sulphur smell can be retained by the print, but this won't be of any consequence to its longevity.
The toning solution can be reused several times. From what I remember, it lasted longer than the ferricyanide bleach and sulphide toner types.
Both RC/PE coated and regular fibre papers can be toned in this bath. However, there are one or two types of paper which won't tone in this bath. All of these were Chinese made papers.