The DARKROOM COOKBOOK, Third Edition

316 THE DARKROOM COOKBOOK
detects the presence of undissolved silver compounds in either negatives or prints. These
can be the result of inadequate fi xing or over-fi xing in which previously dissolved silver is
absorbed into the material.
Distilled water, 100.0 ml
*Sodium sulfi de, anhydrous, 2.0 g
* Be sure to use sodium sulfi de, not sodium sulfi te.
Mix in a well-ventilated area and store in a small stoppered bottle for not more than 3 months.
The dilute solution keeps for a limited time and should be replaced weekly.
Dilute 1:9 with distilled water.
Squeegee the print or negative and place one drop of the solution on a clear area such as
the border (you can use an unexposed negative or print that has been processed in the fi xer
being tested). Wait 2 or 3 minutes then remove any excess solution with a clean white blotter.
Any yellowing, other than a barely visible cream tint, or noticeable brown stain indicates
excess silver in the emulsion. If the test is positive residual silver can be removed by re-fi xing
in fresh hypo and rewashing for the recommended time. The yellow stain from the ST-1 is
permanent.
Alternative Residual Silver Test Solution
An alternative residual test solution can be made from a 10% solution of selenium toner concentrate.
Use this solution in the same way as ST-1. Residual silver is indicated by a red stain.
NOTE: Prints previously toned in sulfi de or selenium toner will not respond to this test
because the residual silver has been toned together with the image.
FORMULA #196
Kodak TC-1
Tray Cleaner
Water, 1.0 liter
*Potassium bichromate, anhydrous, 90.0 g
Sulfuric acid, concentrated, 96.0 ml
* Potassium bichromate is an allergen to some people and a suspected carcinogen. See precautions
under potassium bichromate in Pharmacopoeia.
Store the solution in a stoppered glass bottle away from light. Pour a small volume of
TC-1 into the tray or vessel to be cleaned. Slosh it around so that the solution has access to
all parts of the tray; then pour the solution out and wash the tray thoroughly with water
until all traces of the cleaner disappear. This solution will remove stains caused by oxidation
products of developers as well as some silver and dye stains. It should not be used to clean
hands.
Caution: Add the concentrated sulfuric acid slowly with constant stirring to the cold solution
of the bichromate.