To Turn Blueprints Brown.
Combined Toning And Fixing Baths.
The combined toning and fixing bath consists essentially of five parts—(1) water, the solvent; (2) a soluble salt of gold, such as gold chloride; (3) the fixing agent, sodium thiosulphate; (4) a compound which will readily combine with “nascent” sulphur—i. e., sulphur as it is liberated—this is usually a soluble lead salt, such as the acetate or nitrate, and (5) an auxiliary, such as a sulphocyanide.
The simplest bath was recommended by Dr. John Nicol, and is as follows:
| Sodium thiosulphate | 3 ounces |
| Distilled water | 16 ounces |
| When dissolved, add | |
| Gold chloride | 4 grains |
| Distilled water | 4 fluidrachms |
A bath which contains lead is due to Dr. Vogel, whose name alone is sufficient to warrant confidence in the formula:
| Sodium thiosulphate | 7 ounces |
| Ammonium sulphocyanide | 1 ounce |
| Lead acetate | 67 grains |
| Alum | 1 ounce |
| Gold chloride | 12 grains |
| Distilled water | 35 fluidounces |
A bath which contains no lead is one which has produced excellent results and is due to the experimental research of Dr. Liesegang. It is as follows:
| Ammonium sulphocyanide | 1/4 ounce |
| Sodium chloride | 1 ounce |
| Alum | 1/2 ounce |
| Sodium thiosulphate | 4 ounces |
| Distilled water | 24 fluidounces |
Allow this solution to stand for 24 hours, during which time the precipitated sulphur sinks to the bottom of the vessel; decant or filter, and add