Rodinal mix not mixing

Just mixed up a supposed 250ml batch of Photographic Formulary Rodinal clone and what a mess. The aminophenol was dissolved first in 156ml of water, the metabisulfite added, and mixed well. Nice clear solution, let to room temperature. Solution A per instructions.

125ml of water was added to the potassium hydroxide. Let to room temperature. Solution B per instructions.

A small amount (10ml) of B was added to A. It immediately turned A into a thick creamy gravy. Adding more of B did not render this into anything else. The entire batch is now near 250ml, which is the supposed size of the stock kit according to the instructions.

What went wrong here, and is it salvagable?

Found a similar thread on Photo.net and figured nothing ventured, nothing gained. Kept adding the hydroxide with a syringe until it began to clear. With some precipitate crystals still in solution, the total volume was 260ml. This did not allow for the addition of water to the final solution as suggested in the instructions. I dont suppose that this additional 10ml of volume will make much difference in the 1:100 or 1:50 working dilutions. Or might it?

I have mixed it from scratch and what you describe is exactly what takes place. It eventually clears and if you stop, a few crystals remain in solution. This is the correct mixture. It was not an exact mixture or volume.

I cannot tell you how it performed wrt 'real' Rodinal, as I have no comparison.

PE

PE, I have tagged the problem. The water I was using was slightly acidic, therefore it was buffering both solutions. Mole for mole, it was just enough to increase the working volume of the hydroxide necessary to complete the reaction. Filtered tap water has been great for common powdered developers, but the next jump is toward distilled for custom chemistry.

All these little lessons...

Pragmatist said:

Just mixed up a supposed 250ml batch of Photographic Formulary Rodinal clone and what a mess. The aminophenol was dissolved first in 156ml of water, the metabisulfite added, and mixed well. Nice clear solution, let to room temperature. Solution A per instructions.

125ml of water was added to the potassium hydroxide. Let to room temperature. Solution B per instructions.

A small amount (10ml) of B was added to A. It immediately turned A into a thick creamy gravy. Adding more of B did not render this into anything else. The entire batch is now near 250ml, which is the supposed size of the stock kit according to the instructions.

What went wrong here, and is it salvagable?

Click to expand...

How was the B solution made? Some recipes are wrong and you wind up with a 20% solution of KOH instead of the required 50% solution. This means you have to add too much of B resulting in a greater volume for the final solution.

This happened to me once in a homebrew. I just used the liquid part of the mix and avoided the sludge at the bottom of the bottle. When the volume got too low, I just chucked it.

I ordered some Agfa Rodinal before they stopped production and it is what I'm now using, but I'd go back to the homebrew w/o hesitation.

Pragmatist said:

The water I was using was slightly acidic, therefore it was buffering both solutions. Mole for mole, it was just enough to increase the working volume of the hydroxide necessary to complete the reaction.

Click to expand...

Hold it - think about that again. You're saying you had to add 10 mls of the potassium hydroxide solution to overcome the acidity of your tap water? Using Gerold's value of 50% KOH for this solution, that means your extra 10 mls had 5 g of KOH in it. I'm suspicious that your tap water was acidic enough to require 5 grams of KOH to neutralize a few hundred mLs of water. If so, you have greater problems with your drinking water than this developer issue.

Also, remember that the pH of your water is not directly tied to its buffering capacity. Pure, deionized water will reach pH 5 or so fairly quickly just from exposure to air, which allows it to dissolve a little carbon dioxide from the air and thereby lowering the pH. It has a moderately low pH, but practically no buffering capacity. Unless you actually titrate your water to measure the buffering capacity, you can't really tell what it is.

At this point, I would suggest that the error could be something as simple as the precision of the glassware used to make the solutions...