Stop Bath, Fixer and Washing: The Complete Process

Development gets all the attention. But three steps follow it, and getting them wrong will destroy an image that was developed perfectly. This is the part of the process that separates negatives that last fifty years from negatives that stain in five.

Stop bath: thirty seconds that protect everything after

When the development timer ends, the reaction does not stop. Developer trapped in the emulsion keeps working, and the last thirty seconds of a nine-minute development are exactly the thirty seconds where overdevelopment shows up as blocked highlights.

A two percent acetic acid solution halts development in about ten seconds. It also protects the fixer: developer carried into the fixer is alkaline and slowly exhausts the fixer's acid buffer.

• Dilute 28% acetic acid stock to 2% working strength.
• Keep the stop within 2 °C of the developer — a cold stop causes reticulation.
• Thirty seconds with continuous gentle agitation for film.
• Ten to fifteen seconds for prints.
• Indicator versions turn purple when exhausted; use them if you process irregularly.

If you dislike the smell — and it is a genuinely unpleasant smell — a plain water rinse at the same temperature is an acceptable substitute. It is less effective at stopping development instantly and it does not protect the fixer, but it is far better than nothing.

Fixer: the step that makes the image permanent

After development the emulsion still contains all the silver halide that was never exposed. It is still light-sensitive. Fixer dissolves it, converting insoluble silver halide into soluble complexes that the wash can remove.

Rapid fixers based on ammonium thiosulfate work in three to five minutes. Traditional sodium thiosulfate takes ten to fifteen. For archival work the two-bath method is the standard: half the fixing time in bath one, half in bath two. Bath one does the bulk of the work and becomes loaded with silver; bath two stays nearly fresh and finishes the job properly.

Washing: where most people stop too early

Fixer that stays in the emulsion keeps working. Thiosulfate slowly converts to silver sulfide, and silver sulfide is brown and permanent. A print that was not washed properly does not look wrong when you make it; it looks wrong in ten years.

Washing works by diffusion, and diffusion slows dramatically once the water immediately next to the emulsion is saturated. That is why a stack of prints in still water will not wash, and why running water matters more than soaking time.

• Film: 5 minutes in running water, or 10 minutes with several changes.
• RC paper: 2–4 minutes in running water.
• Fibre paper: 30 minutes in running water, or 15 minutes after hypo clear.
• Water temperature: 18–24 °C, within 3 °C of the chemistry.
• Hypo clear before the wash roughly halves the required time.

The final rinse and drying

The last step is a wetting agent: one drop per 200 ml, thirty seconds, no agitation, no rinse afterwards. It breaks the surface tension so the water sheets off the film evenly instead of beading, and beading is what leaves drying marks.

Hang the strip with a weighted clip at the bottom, in still, dust-free air, and leave it for two to four hours. Never use heat. Dust baked into a warm emulsion cannot be removed.

The complete schedule

Anyone can develop a negative. The discipline is in the three steps afterwards.