Ryuji said:
I don't know why you have to invoke superadditivity in the context of sulfite "substitute" but the above statement is flawed. Superadditivity is defined as the rate of development of multiple developing agents is greater than the sum of that of each agent alone. Both sulfite and ascorbate will give rate of development of zero or very close to zero. Between the two combinations mentioned in the quoted text, the version containing ascorbate should give at least as much rate of development as the one lacking ascorbate as sulfite, depending on the emulsion and exposure, when pH and other vital conditions are made equal.
The primary reason why sulfite is used in developer solution is to preserve the solution. Superadditivity is not even requirement for a useful developer. Plus, the reason why superadditivity is more significant in sulfited developer solutions containing hydroxybenzene agents is that sulfite inhibits development by said agents. Thus taking sulfite out and throwing something in to argue this new stuff works as fine as sulfite based on superadditivity doesn't make sense.
Putting aside for the moment other considerations, here is my experience with the use of ascorbic and sulfite in a pyrocatechin + phenidone or metol or p-aminophenol formula.
1. The addition of small amounts of either ascorbic or sulfite to a working solution gives a significant increase in energy level, or activity. That amount has been found to be, by experiment, on the order of about .04g of ascorbic per liter of working, and about .15g of sulfite per liter of working. I have in the past attributed this increase in synergism to superadditivity. Perhaps it is something else, but the increase in activity is quite real. The secondary reducer of either phenidone or metol or p-aminophenol seems to plays an essential role in this increase in synergim because it does not take place with pyrocatechin + ascorbic by itself.
2. The addition of either ascorbic or sulfite in the amount noted above also decreases stain, or overall B+F, slightly.
3. Increasing the amount of either ascorbic or sulfite by about 3X-4X the above amount results in even greater energy or activity, but at some point the stain completely disappears. And the loss of stain is abrupt rather than gradual.
4. The use of ascorbic in place of sulfite in the Pyrocat-M formula, at the rate noted above, appears to give lower B+F, or general stain, with very long development times. This has been especially evident when measurements are done in UV mode. However, as a caveat I will note that there have been some anomalous results from different stock solutions.
5. Other than what has been noted above I do not find much difference, at least from the point of view of sensitometry, in the use of ascorbic or sulfite in the Pyrocat-M formula (pyrocatechin + metol). Granted, tank life is not an issue for me since this developer should be used as one-shot and discard, since when used this way tank life of both solutions is at least a couple of hours
Sandy
