Back when I was still using D-76 I found an 8oz bottle of stock in the back of my cabinet with a three year old label on it, it still worked like fresh.
Wouldn't it be much easier to buy ID-11 in 1 litre packages and mix as needed? Kodak says mixed D76 in full, tightly closed bottles has a life of 6 months, not "years"
I used this developer a lot in the past but did not do extensive testing here on carryover but @gorbas did some testing and shared his results. This was the result of a 1L Thornton developer that had been been used for ten rolls. https://www.photrio.com/forum/threads/advice-on-my-two-bath-developer.181701/page-7#post-2423623
"Incidentally, Bath A, without an alkali activator, lasts a long long time in a well sealed bottle — much longer than conventional developer. A year is not uncommon. All that happens is that a small amount is absorbed by each film, developer, and the volume is slightly decreased each time of use. Replenishment is unnecessary. 15 films per litre are easily developed before replacement. Bath B discolors because of oxidised traces of Bath A in it, but this does not reduce its effectiveness. Again 15 films per litre are easily achieved."
There is a bit of a jump in logic here.In any case, this type of two-solution development is subject to all the same variables as regular/single-solution development - and more, so the notion it is easier or foolproof is misguided.
There is a bit of a jump in logic here.
Does it have more variables? Yes.
But that does not tell you whether it is easier or harder to use. What matters is how precisely I need to control those variables. If I get the time wrong by 10% will be effect be larger in BTTB than if I had used D76?
Now, I don't know the answer to that question. But the Tri-X data sheet changes D76 times in +20% increments to show noticeable changes in the density curve, while John Finch increased BTTB times in +50% increments to produce what, to my novice eyes, looked like small changes.
In any event, I will certainly get to compare the experience with D23 vs BTTB, so I'll get to see for myself if one is easier and if the difference matters.
@dcy used it in post #52.Had to look it up.
@dcy used it in post #52.
I know. Two people using an expression I had never heard before... bugged the hell out of me.
an expression I had never heard before.
“Assuming a 135 film contains 0.3g of silver, with 25% being developed, this would consume 0.12g of Metol (sulfate).”
BUT even after 15 films there is probably enough metol in the remaining 700ml to develop another 28 films.
NOTE: I’d be grateful if someone could check my calculations.
A good model! We can assume that x% of development occurs in Bath A, with the remaining (100–x)% in Bath B.That excess availability of metol prompts me to mention how I use BT2B, and possibly(?) one reason why I have never noticed any serious change in negatives with increasing film count. I have always felt that my role in Bath A was to keep the film supplied with developer molecules, whereas in Bath B it was to oblige the film to make full use of what it had absorbed. So in Bath A I do continuous inversion agitation, just as you would when developing a print; but rather little agitation in Bath B.
@snusmumriken: Concentration of the developing agent matters. Even though a roll might consume only 0.12 g of Metol, such ridiculously small amount by itself wouldn't be able to develop the roll fully at the pH of Thornton Part A even after an hour in the first bath. To get substantial development in the 4-5 minutes the film spends in the first bath, concentration of Metol needs to be significantly more than the actual amount of Metol consumed by one roll and hence Thornton used 6.25-6.5 g. As you have calculated, the concentration of Metol in Part A slowly but surely goes down after every roll and might need longer development time to compensate for the loss after a few rolls.
In your story I think the implicit assumption is that the metol carried over from A to B in the swelled emulsion is used to develop silver. Given the lack of an anti-oxidant in B (apart from carried over sulfite from A), I'd expect any carried-over metol in B to oxidize fairly rapidly.Maybe this is compensated by the increasing concentration of metol in Bath B?
I'd have thought the dry emulsion becomes saturated with solution within seconds of immersion. After that, it's a matter of agitation to avoid local depletion/inhibition, diffusion through the already-saturated emulsion, and time to build up the image. My understanding is that - compared with other developing agents - metol is particularly good at initiating the development of exposed silver grains, but builds density slowly, especially in a mildly alkaline solution like Bath A. You get a full but flat image by the end of Bath A, as @gorbas experiment showed.This, of course, ignores the critical fact that Part A is supposed to saturate the emulsion. For all I know, the emulsion was already saturated after 3 minutes, in which case letting the film sit in Part A for 5 min will always be more than enough for all 15 rolls of film.
I didn't actually make that jump between Bath B carry-over and developing activity, but yes, that is what worries people. In reality, one can return to the darkroom after weeks of absence to find Bath B has become a vivid orange due to oxidation of the carried-over metol. It still does its job.In your story I think the implicit assumption is that the metol carried over from A to B in the swelled emulsion is used to develop silver. Given the lack of an anti-oxidant in B (apart from carried over sulfite from A), I'd expect any carried-over metol in B to oxidize fairly rapidly.
I agree with your conclusion that the activity will shift and I expect that densitometry on some properly controlled test strips will show this.
It still does its job.
I think that part doesn't quite hold true and in practice will turn out to be more complex.Maybe this is compensated by the increasing concentration of metol in Bath B? The same calculations suggest that after 10 films the concentration of metol in Bath B would be about 24% of that in Bath A, if we assume that the overall volume of Bath B doesn’t change (because the saturated film carries as much liquid out as it carries in).
I think you are misunderstanding what I was trying to do. I wanted to know whether there was any basis for thinking that the depletion of metol in Part A, and the carry-over of metol into Part B, were substantial, quantitatively. If (in the worst case) the metol in Bath B remained active, then potentially it could reach quite a significant concentration. I was not making any kind of argumentSure. But how much viable metol is in it at that point? That's what part of your argument relied on:
I think that part doesn't quite hold true and in practice will turn out to be more complex.
Just as an aside, a lot of the carryover is from the liquid sitting on the surface of the film, the walls of the tank, and in the reels. It's not mostly from in the emulsion. Sulfite is also getting carried over, though also in small amounts.In your story I think the implicit assumption is that the metol carried over from A to B in the swelled emulsion is used to develop silver. Given the lack of an anti-oxidant in B (apart from carried over sulfite from A), I'd expect any carried-over metol in B to oxidize fairly rapidly.
I can do that! Let's hope I never accidentally pour the fixer in first.
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