Versatile Tanning and Stopping Bath
A tanning bath for damaged or “delicate” emulsions—and as a standard replacement for a regular stop bath.
About the foot bath
This bath is primarily intended for photographic materials with damaged, “delicate,” or weakened emulsions, but it can be used as a standard stop bath with any films or papers. Thanks to its tanning effect, subsequent solutions can be used at temperatures up to 25 °C, the drying time is reduced by a factor of 2–3, and damage to or melting of the photographic paper’s emulsion during hot glossing is virtually eliminated. It is not recommended to place materials in this bath without an intermediate rinse if development was performed in a strongly alkaline developer—alkali entering the acidic tanning bath may cause localized precipitation.
How to Prepare and Use
- 1Dissolve potassium aluminum alum (20 g) in 400–450 mL of distilled water at a temperature of 25–30 °C, stirring constantly until completely dissolved.
- 2In a separate container, using the same amount of water at the same temperature, dissolve boric acid (8 g) and potassium metabisulfite (10 g)—the contents of the second packet.
- 3Wait until both solutions have completely dissolved and cooled to room temperature (20–25 °C).
- 4Combine the two solutions and add distilled water to bring the total volume to 1 liter. Filter if necessary.
- 5Process the photographic material immediately after the developer for 0.5–2 minutes to stop development and perform a light tanning.
- 6For a stronger tanning effect, increase the treatment time to 5–7 minutes. The standard operating temperature of the solution is 20 °C.
Pros
- Allows for further processing at elevated temperatures (up to 25 °C)
- Reduces the material's drying time by a factor of 2–3
- Protects damaged and weakened emulsions
- The prepared solution can be stored for up to 1 year
Cons
- Doubling makes subsequent rinsing more difficult and may slow down the removal of the fixative
- Not suitable for materials that do not require intermediate rinsing after a strongly alkaline developer
- A partially used solution lasts only about 3 weeks
Recipe for 1 liter
The solution is prepared from two separate packets: the first contains alum, and the second contains boric acid and potassium metabisulfite. Dissolve each one separately in 400–450 mL of warm (25–30 °C) water, wait for them to cool to room temperature, and only then combine them, adding distilled water to bring the total volume to 1 L.
Chemical structures: PubChem (public domain)