sodium thiosulfate and b/w resersal question

[holmburgers]

sodium thiosulfate or sodium/potassium thiocyanate rob an emulsion of it's potential if it is used in a reversal B&W process... regards, dw

This is a revelation, and from someone knowledgable enough to know the real deal. Very interesting...

 

[Gerald C Koch]

This is a revelation, and from someone knowledgable enough to know the real deal. Very interesting...

Revelation BUT no specific solution.

 

[holmburgers]

As he is wont to do... (afterall, he has a business to run)

 

[Photo Engineer]

Do not use Ammonium Thiosulfate.

There are many solutions to this problem, but some silver halide solvent is going to be needed.

PE

 

[hrst]

Even though you CAN NOT and MUST NOT use rapid fixer instead of hypo, you can still give it a shot . The point is, the amount of thiosulphate needed will be so low that the level of unwanted chemicals will be low also; you will be using just a few milliliters of concentrate per liter or so! I would think the ammonium ion is the biggest problem. But it's not going to explode so feel free to experiment...

Why I am telling this is because I have done this. When I was starting up in film photography, I experimented on reversal processing BW paper to create prints from color slides. As I didn't have plain hypo, I just poured a bit of fixer to the developer. It didn't explode, I didn't die and I liked the results; but no side-to-side comparisons done without the fixer!

 

[Photo Engineer]

Oh, the Ammonia is the bad actor if you use Ammonium Hypo. It effectively increases the activity of the halide solvent. It also increases the chance of fog and especially dichroic fog.

PE

 

[cliveh]

Do not use Ammonium Thiosulfate.

There are many solutions to this problem, but some silver halide solvent is going to be needed.

PE

Good advice, stick to Sodium Thiosulfate

 

[nworth]

Sodium thiosulfate was used in some early (1920 era) reversal processes, but it was somewhat tricky and often lend to fog. It is a silver solvent, needed in the first developer to produce a clear image. Sodium (or potassium) thiocyanate was found to be a better and more reliable solvent for this use. As noted above, ammonium compounds are generally bad actors in developers.