Photo Engineer said:
If you would just give my calculations a try, you would see that. PE
Ok. Here's what I get from your setup.
"Calculate the moles per square meter of HBr released in this volume and then calculate the amount of Na2CO3 present and ascorbate present if the carbonate is at 50 g/l and the ascorbate is at 5 g/l."
The HBr is equal to AgBr assuming 100% reaction, so that gives 0.01065 mole HBr/m^2. With the thichness of 0.05mm, that gives a volume of 50 ml for that 1 m^2 sheet of film.
So now are you assuming the CO3= will go into that 50 ml of emulsion at a concentration of 50g/L. That's 0.833 mole/L which means there is 2.5 g CO3= in the 50 ml of emulsion, or .04165 mole CO3= total in the emulsion. That's 3.9 times more moles of CO3= than HBr, or H+ from the acid. And of course, we now need to go to normality, and there is 7.8 more equivalents of CO3= than the H+ from the HBr.
For Ascorbate, 5g/L gives 0.0257 mole/L which gives 0.00143 mole in the emulsion. There's 7.6 times more HBr in the emulsion than there is ascorbate in the emulsion from the solution. (This assumes they all stay there during the development, no diffusion of H+ or Br-, or the other compounds in solution)
This all assumes that the carbonate and ascorbate can dissolve into the emulsion at the same concs that they are on the solution (i.e the gelatin has no volume in the swelled emulsion?).
One thing to remember is that 50 g/L CO3= is pretty strong for any developer, at least for a "stand" developer. The Pyrocat will be much less - 20 mls of 75% K2CO3 per litre at a 1+1+100 dilution. 2 or more times less for what people are using in stand developers. You'll not have an excess of CO3= in those solutions. And much less hydroxide for people using Rodinal.
Of course, the HBr will actually not reach the concs discussed above in your example due to diffusion as it is not all developed at the same time, but that brings me back to my original point - a stronger buffer may help speed the "stand" process along and it should allow less time for the HBr to diffuse out or fresh buffer to diffuse in...
And that's why I'm guessing the this approach should help with the kinetic gradient to use for increasing the edge effects.