ferrous sulfate + washing soda developer, clearing bath for dichromate bleach

[noofzz]

Hello!!

I was looking for alternative to sulphite clearing bath and tried ferrous sulfate. It worked but i needed to neutralize sulphuric acid too, so i mixed sulphate and baking soda. The solution began to "boil" yielding greenish settling. Don't know why, but i decided to put exposed photopaper there, to the boiling reaction. It developed paper!!
I tried collodion developer (ferrous sulphate+acetic acid+alcohol) with paper, it doesn't work......untill you add enough soda and start the same boiling reaction.
And the solution doesn't work after the reaction stops (left paper for whole night).

So i'm wondering, what actually develops silver in this case?
And is there any alternatives to sulphite clearing bath after dichromate bleach, especially that can be bought not only at a chemicals store?

 

[bernard_L]

Possibly the conversion (oxidation) of Fe2+ ion to ferric Fe3+. Apparently the pH also matters, like for regular developers.
Interesting!

To answer (maybe) your question I found that to completely clear film that went through dichromate+1%HCl (first step of intensification) a 1% solution of sodium or potassium carbonate (following a pre-wash) works well, achieving a level of clearing that could not be reached with repeated water washes. Curious to know if that works for you.

 

[Rudeofus]

Yes, Ferrous ion is a photographic developer and AFAIK used in some alternative processes. Since it can be freely mixed with Ferric ion to obtain adjustable reduction potential, it was also used in scientific literature to measure the effect of reduction potential on photographic properties. Ferrous Sulfate also develops film/paper in acidic state. If you make Ferrous Sulfate (or almost any Ferrous or Ferric salt FWIW) too alkaline, you will precipitate Ferrous/Ferric Hydroxide, that's likely the green precipitate you saw.

I am surprised to read that Ferrous Sulfate didn't develop when mixed with Acetic Acid, since Waldack’s Formula No. 1 (same link as above) seem to work just like that.

There are many reasons for using Sulfite in clearing bathes:

• It reduces and thereby inactivates strong oxidizers (Ferricyanide, Dichromate)
• Despite being a strong reducer, it does not develop Silver by itself
• It scavenges oxidized developers like Quinone and Quinonediimine and can therefore be used in color processes before bleaching.
• Silver Sulfate is somewhat soluble, therefore neither Sulfite, not its oxidation product will significantly interfere with following processing steps.

 

[Gerald C Koch]

Ferrous sulfate will not make a very good clearing bath. The chemistry of sulfates is different from that of sulfites although the names can be confusing. Adding sodium carbonate to a solution of ferrous sulfate will result in the precipitation of what is commonly referred to a ferrous carbonate. This is not a simple chemical but a rather complex mixture. Your best bet is to stay with a recommended clearing bath.

 

[noofzz]

Gerald, I used ferrous sulfate because I read somewhere that it neutrilizes dicromate ( 6FeSO4 + K2Cr2O7 + 7H2O = 5Fe(OH)SO4 + Fe(OH)3 + K2SO4 + 2Cr(OH)3 )........ then I decided to add some baking soda (what i have at home ( Sodium Hidrocarbonate)) to neutralize sulphuric acid from the bleaching solution too.

 

[Gerald C Koch]

Gerald, I used ferrous sulfate because I read somewhere that it neutrilizes dicromate ( 6FeSO4 + K2Cr2O7 + 7H2O = 5Fe(OH)SO4 + Fe(OH)3 + K2SO4 + 2Cr(OH)3 )........ then I decided to add some baking soda (what i have at home ( Sodium Hidrocarbonate)) to neutralize sulphuric acid from the bleaching solution too.

Ferrous sulfate is acidic in in its reaction. Then there is the added acid in the bleach. How did the solution suddenly become basic enough to produce the iron and chromium hydroxides? Fe II ion will convert chromium VI to chromium III in the presence of acid.

 

[Rudeofus]

noofz, you used the term "neutralize" both to describe "stops oxidation by Potassium Bichromate", and in the sense of "brings pH towards 7", and thereby got confused in the process. Adding baking soda to his mix obviously didn't help your cause, creating a precipitate instead.

Is there any particular reason you don't want to use Sulfite for your clearing bath?