I developed with Caffenol for the first time tonight, using the Delta Standard recipe I found online. Developing went fine. I had a bit of trouble loading the film, but I got it.

The problem happened with the stop bath. I poured the Caffenol down the drain, didn't wash the tank, then poured inside it what I normally use as a stop bath, which is citric acid (I've always developed with D-76 before, and had no problems using it).

I started to agitate and noticed the tank got stuffed, as if it were filling up with air, like a balloon. I agitated once more and it almost exploded. The lid simply sprung open. Luckily, I was agitating in the bathroom and didn't mess anything up with the liquid that leaked, but I got fogs/light leaks on my negative, and I'm thinking it had something to do with this.

I was wondering what might have caused that?

  • 1
    \$\begingroup\$ Is it possible baking soda was used in lieu of washing soda? \$\endgroup\$ Nov 22, 2020 at 12:00
  • \$\begingroup\$ I think it is washing soda. I bought it at a pool supplier shop. The only ingredient listed is sodium carbonate. I checked twice to confirm. I can't be 100% sure, though. \$\endgroup\$
    – J J Benez
    Nov 22, 2020 at 15:55
  • \$\begingroup\$ Have you considered mixing the chemicals in daylight without film to see what happens? \$\endgroup\$ Nov 22, 2020 at 16:15
  • \$\begingroup\$ I did not consider that. I will try it and report the results. \$\endgroup\$
    – J J Benez
    Nov 22, 2020 at 16:16

2 Answers 2


When an acid solution such as citric acid and an alkaline solution such as Caffenol developer are combined, chemical neutralization results. A salt solution is the product and carbon dioxide gas is liberated (abundantly). Similar reactions occur in baking. Such reactions cause bread and biscuit to rise (leavening). Let me add, generation of gasses during film developing should be controlled. That's why we normally use a dilute solution of acetic acid (vinegar) as the stop bath. What can happen is, blisters often form within the film emulsion if the stop is too strong. This action will spoil the film. Let me add, development takes place in an alkaline environment (some exceptions). You can use plain water rinse to purge the developer or a mild acid rinse. Acetic acid is preferred if developing is to be halted quickly. Acetic acid is one of the ingredients of the fixer; thus we use it to not only stop developing but to reduce fixer contamination with carryover developer.


Going from developer to stopper means going from basic to acidic milieu. Washing soda is basic because it is a salt of sodium from a comparatively weak acid. If you add a stronger acid, like citric acid, it will cause the carbonate ions (CO3--) to get protonised and then essentially fall apart into CO2 and H2O, with the carbon dioxide bubbling out.

In contrast, caustic soda used for generating basic milieu has OH- ions to start with, and protonising those just results in H2O which remains in solution.

Personally, my private guess would be that a basic agent that tends to bubble when neutralised is a bad idea for working with film emulsions but that's nothing more than a gut feeling without any supporting experiments of my own.

When combining the agents you mention, this reaction is expected. But I would think that the person designing this workflow did not intend for large amounts of agents to be combined in this manner.

  • \$\begingroup\$ What, exactly, does "basic" mean ? "using the same container for different agents in succession also seems like asking for trouble" Have you done any film developing? \$\endgroup\$
    – Alaska Man
    Nov 22, 2020 at 21:38
  • \$\begingroup\$ @AlaskaMan Yes, I did stuff in the lab, but you are right that I have been mixing up film and paper development in my head. Will fix that. "basic" is the opposite of "acidic". I really have no good synonym for that rather basic chemistry term. \$\endgroup\$
    – user95069
    Nov 23, 2020 at 0:02

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