The blue color may be totally removed at any time by placing the print in ammonia water.
This is the standard formula.
ANOTHER PROCESS FOR BLUE PRINTS.
Float the paper for a minute in a solution of
| Ferridcyanide of potash | 1 ounce. |
| Water | 5 ounces. |
Dry in a dark room, and then expose beneath a negative until the dark shades have assumed a deep blue color, then immerse the print in a solution of
| Water | 2 ounces. |
| Bichloride mercury | 1 grain. |
Wash the print, and then immerse it in a hot solution of
| Oxalic acid | 4 drachms. |
| Water | 4 ounces. |
Wash again, and dry.