Why Proper Washing Matters
After fixing, film and paper retain thiosulfate (hypo) compounds in the gelatin emulsion and paper fibers. If not removed, residual thiosulfate slowly reacts with the silver image over months and years, producing yellowish-brown stains and fading. Proper washing is essential for archival permanence.
The Chemistry of Washing
Washing removes thiosulfate by diffusion: the thiosulfate-laden solution in the gelatin gradually exchanges with fresh water. This is a logarithmic process -- each change of water removes a fixed percentage of the remaining thiosulfate. This means many short wash cycles are far more efficient than one long soak.
Ilford Archival Washing Method (Film)
The most efficient method, recommended by Ilford:
- Fill the tank with water at processing temperature
- Invert 5 times, pour out
- Fill again, invert 10 times, pour out
- Fill again, invert 20 times, pour out
- Drain and hang to dry
Total water use: approximately 1.5 liters. Total time: about 5 minutes. This method removes thiosulfate as effectively as 20-30 minutes of running water washing.
Running Water Wash (Film)
The traditional method:
- Insert a hose into the center of the tank reel
- Run water at a moderate flow rate for 10-15 minutes (with a washing aid) or 20-30 minutes (without)
- Ensure the water reaches all surfaces by checking that it overflows freely
Washing Prints
RC (Resin-Coated) Paper
RC paper has a waterproof base that prevents thiosulfate from penetrating deeply. Wash for 4-5 minutes in running water. Over-washing RC paper does not help and can cause the emulsion to separate from the base.
Fiber-Based Paper
Fiber paper absorbs thiosulfate deep into its cellulose fibers. Without a washing aid, fiber prints require 60 minutes or more of running water for archival permanence.
With a washing aid (Hypo Clearing Agent):
- Fix the print
- Rinse briefly
- Soak in hypo clearing agent for 2-3 minutes
- Wash in running water for 10-20 minutes
The washing aid converts thiosulfate into more easily washed-out compounds, dramatically reducing wash time and water use.
Hypo Elimination Testing
To verify washing effectiveness, test a small area of the print margin with residual hypo test solution (Kodak HT-2 or equivalent). A stain indicates insufficient washing.
HT-2 test solution:
- 750ml distilled water
- 125ml 28% acetic acid
- 7.5g silver nitrate
- Water to make 1 liter
Apply a drop to the white margin. Compare the resulting stain against the reference chart after 2 minutes.
Tips
- Water temperature during washing should be within 3C (5F) of processing temperature to avoid reticulation.
- A squeeze/Film drain clip removes excess water before hanging, reducing drying marks.
- A drop of Photo-Flo in the final rinse prevents water spots by reducing surface tension.
- Store negatives in archival sleeves after they are completely dry. Never store damp negatives.
- Hard water can leave mineral deposits on film. If your water is very hard, use a final rinse of distilled water with Photo-Flo.