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I'm interested in DIY photo development and I came across a reversal process that uses chemicals easily available at the grocery store. The purpose of a reversal process is to take a partially developed negative, which is a suspension of silver and silver bromide in gelatin, and turn it into a positive by removing the silver and leaving the silver bromide behind.

The two in question are 3% hydrogen peroxide and 5% acetic acid. I have tried this and it works but I don't understand why.

The process is as follows:

  1. 30ml of 5% acetic acid solution is added to 500ml of 3% hydrogen peroxide, the rest is just water.
  2. The mixture is then heated to 60°C.
  3. In complete darkness the partially developed film is placed in the liquid for 6-10 minutes.
  4. After this the silver is gone, but a yellow tint is left behind.
  5. After this the silver bromide is then exposed and redeveloped leaving a positive image.

I believe the tint is silver oxide but I am unsure as I don't know enough about what is actually taking place in this reaction. I'm left with all sorts of questions:

  1. What reaction is taking place to remove the silver?
  2. What other reactions might be happening?
  3. What is the fate of the removed silver after this reaction?
  4. Why does it need to be hot?
  5. Why is there a yellow tint left behind? Is it silver oxide or acetate, and how might it be removed/avoided?

Fully developed film

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The slow reaction dissolving silver must be : $$\ce{2Ag + H2O2 + 2CH3COOH -> 2CH3COOAg + 2 H2O}$$ The mixture has to be hot because the rection is extremely slow. Its rate is negligible at room temperature. Even at $60$°C, about $10$ minutes are required to dissolve nanoparticles of silver on the milligram scale. Silver acetate $\ce{CH3COOAg}$ is moderately soluble in water ($\pu{10 g/L}$).

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The acetic acid stops the developer, and the hydrogen peroxide oxidizes the silver particles that were selectively reduced by the developer. More detail in this thread enter link description here. Probably needs to be hot just to force an acceptable reaction rate from the peroxide, or to get any reaction at all. The yellow tint is likely just the natural color of the silver halide in the original film. I doubt the tint can be removed, but the remaining silver halide, having been so treated in the dark, should still be light sensitive, so you may try exposing it to light, then developing normally to see if the silver halide gets reduced to silver, leaving the normal black.

Using a fixer would probably complex & remove the silver halide, leaving blank film.

If you want a positive, you could develop the negative film normally, then "contact print" to a fresh piece of negative film, which you then develop normally.

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    $\begingroup$ Thanks, but I don't think the yellow is Silver Halide. The image you see above is actually after re-exposure & redevelopment and then fixed to remove any possible residual halides. The yellow is actually in areas where the silver has been removed, and where the halides have been converted by the first developer. This leads me to believe that the yellow color comes from a compound produced during the bleaching process. $\endgroup$
    – BathroomFilmLab
    Jun 8, 2021 at 16:36
  • $\begingroup$ Don't you think that this yellow color may be due to the gelatin or the film itself getting old and somewhat oxidized without any silver compound involved ? $\endgroup$
    – Maurice
    Jul 9, 2021 at 8:09

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