Next to this, as regards ease of manipulation, the tungstate bath may be placed, the following being a good formula:
| Sodium tungstate | 40 grains |
| Gold chloride | 2 grains |
| Water | 12 ounces |
The prints should be toned a little further than required, as they change color, though only slightly, in the hypo. {541}
Provided that ordinary care be exercised, the sulphocyanide bath cannot well be improved upon. The formulas given by the various makers for their respective papers are all satisfactory, and differ very little. One that always acts well is
| Ammonium sulphocyanide | 28 grains |
| Distilled water | 16 ounces |
| Gold chloride | 2 1/2 grains |
For those who care to try the various baths, and to compare their results, here is a table showing the quantities of different agents that may be used with sufficient water to make up 10 ounces:
| Gold chloride, 1 gr. to 1 oz. water | 12 dr. | 16 dr. | 16 dr. | 11 dr. | 11 dr. | 14 dr. |
| Borax | 60 gr. | |||||
| Sod. bicarbonate | 10 gr. | |||||
| Sod. carbonate | 20 gr. | |||||
| Sod. phosphate | 20 gr. | |||||
| Sod. tungstate | 40 gr. | |||||
| Amm. sulphocyanide | 17.5 gr. |
We may take it that any of these substances reduce gold trichloride, AuCl3 to AuCl; this AuCl apparently acts as an electrolyte, from which gold is deposited on the silver of the image, and at the same time a small quantity of silver combines with the chlorine of the gold chloride thus:
AuCl + Ag = AgCl + Au
When toning has been completed, the prints are washed and placed in the fixing bath, when the sodium thiosulphate present dissolves any silver chloride that has not been affected by light.