Replenished D23 and development times

Hello,

I've started using D23 recently and I will shortly begin replenishing my litre bottle with DK-25R. On John Finch's Pictorial Planet website, and if I'm not misunderstanding anything, he writes that once the cycle of replenishment is initiated, development times should be increased by 10% for most films, and in his experience, 30% with HP5+ (a film that I use regularly). Why would this be? I would have thought that the replenishment with a solution containing more metol would speed up development, but there must be more to it. Is it to do with a change in alkalinity?

This is the page that I'm referring to:


Cheers,

I don't know the scientific explanation for his recommendation, although I think it has to do with the fact the the replenisher doesn't fully compensate for the exhaustion the developer has experienced. More experienced and chemically proficient members can answer this question better than I can.

I also read Finch's comment when I started to use replenished D-23, but decided to keep the same time as the one that I had adopted for stock solution D-23, which, for me, is about 15% more than the time for D-76.

I'm no expert on the matter and haven't done extensive tests, but from what I understand, slight overdevelopment with D-23 will not affect the highlights — i.e., risk of blown highlights — as with other developers such as D-76 or Xtol. It will, however, affect contrast. D-23 not being a high-contrast developer, it is possible that, to John Finch's taste, the extended time becomes preferable. I prefer to control constrast through agitation.

Then there is the matter of how you rate you film. For me, HP5+ works in D-23 at ISO 250.

That said, I have realized that with D-23 times, you do have to apply the "better safe than sorry" principle. There is loss of speed with this developer, and with underdevelopment there is a strong chance of ruining your film. I found that to be true the few times I used it with Tri-X (rated at 400, though), which needed a higher percentage of added time than HP5+.

Alex Benjamin said:

I don't know the scientific explanation for his recommendation, although I think it has to do with the fact the the replenisher doesn't fully compensate for the exhaustion the developer has experienced

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The other very real possibility is that the amount one loses to carry-over or discards as a part of the replenishment regime isn't sufficient to remove enough of the development byproducts to compensate for the effects of byproduct build-up.
Replenishment is a two part process - replace lost activity, and remove byproduct build-up. It is relatively difficult to design a replenishment regime that compensates for both issues with a single replenishment action.

Bromide picked up from the film into the developer is what I understand to be the main cause. Replenisher replaced the oxidized metol and increases alklinity to compensate for the loss of pH due to that oxidation -- but the steady state reached by replenishing seasoned developer isn't the same as using fresh developer as a one-shot, and that's mainly due to bromide in solution acting as a restrainer. This is also the main reason for adding time when you reuse stock solution without replenishment (along with oxidation of developing agents and loss of pH, of course).

Donald Qualls said:

Bromide picked up from the film into the developer is what I understand to be the main cause. Replenisher replaced the oxidized metol and increases alklinity to compensate for the loss of pH due to that oxidation -- but the steady state reached by replenishing seasoned developer isn't the same as using fresh developer as a one-shot, and that's mainly due to bromide in solution acting as a restrainer. This is also the main reason for adding time when you reuse stock solution without replenishment (along with oxidation of developing agents and loss of pH, of course).

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I see, thanks a lot, that makes a lot of sense

MattKing said:

The other very real possibility is that the amount one loses to carry-over or discards as a part of the replenishment regime isn't sufficient to remove enough of the development byproducts to compensate for the effects of byproduct build-up.

Click to expand...

Donald Qualls said:

Replenisher replaced the oxidized metol and increases alklinity to compensate for the loss of pH due to that oxidation -- but the steady state reached by replenishing seasoned developer isn't the same as using fresh developer as a one-shot, and that's mainly due to bromide in solution acting as a restrainer.

Click to expand...

Yep, with film the main development byproduct of concern is probably bromide ion. I don't personally have too much experience with B&W materials in this respect, but my understanding, via literature, is that Metol is only moderately affected by bromide ion. So I would guess that this is a main reason why D-23 replenishment works as well as it does.

The ideal developer, if designed for replenishment, would already include a significant amount of bromide in the formula. This would allow a special replenisher - one with essentially NO bromide in it - to dilute the used developer (with additional bromide added as a development byproduct) back down to the original bromide concentration. This is, in fact, how the C-41 (color negative) process works.

FWIW many modern films also include a small amount of silver iodide, releasing iodide ion as a development byproduct. Iodide seems to be a much stronger restrainer than bromide, so perhaps this could explain why some films seem to need even more added development time. Just a wild guess on my part.

Tabular grain films have iodide; its lower reaction rate with thiosulfate is responsible for fixing being very slow and sometimes incomplete if these films (Delta, T-Max, Acros, possibly Foma 200) are fixed with sodium thiosulfate vs. ammonium thiosulfate (no, I don't know the chemistry behind why one works better than the other). The effect of iodide in developers is already accounted for in the one-shot development times for these films, and phenidone seems less prone to this effect even than metol.

I don't hear about a lot of folks developing tabular films in D-23, but I'd guess you'll see more loss of activity over a period of replenishment with these films. For myself, I've only used D-23 on conventional grain films -- mostly Fomapan, come to that.