How do you know when to stop reusing a developer?

[Rick A]

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"

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.

 

[dcy]

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

Thank you for sharing that link. I've been reading that thread --- btw, it's so cool you made your own developer and got such good results!

I didn't read every comment getting into all the weeds of all the chemistry, but I followed the high-level discussion and I was quite interested in @gorbas 's comparison. Seeing a concrete example after 10 rolls really gives me better sense of what to expect and what sort of issues we're talking about.

Yeah, I can see that Part B really did become a developer in its own right. It's weird that either A or B alone can develop an image. Yet, somehow, the image with the full A + B baths still looks fine.

I was interested in @Raghu Kuvempunagar's observation that Part A loses strength at the same time that B becomes a developer of its own. Maybe the longevity of A+B together is longer than you'd guess from just seeing how A and B change individually.

 

[john_s]

When using the Thornton 2-Bath repeatedly, as the first developer becomes a bit weaker, the Part_2 gradually becomes a developer in its own right, compensating for the loss in Part_1. Maybe variations occur due to different amounts of carry over (maybe some tank setups drain better than others?). Just a guess.

 

[dcy]

Digging more through the Photrio archives, I found that less than a year ago @Alex Benjamin posted an excerpt from Barry Thornton's Edge of Darkness. I reproduce a small portion of that here.

Here's what Thornton says about this developer:

"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."

 

[BMbikerider]

Basically I doi not reuse any developer. In the world of photography developer for B&W is probably the cheapest of all the elements involved so why waste film if the reuse of developer may result in under development. Apart from that there is the effort to get out there and see something worth while photographing.
Even with C41 colour I have always used once then discarded. A little more expensive- agreed but that takes away the risk of getting something tthat is not as good as it could be. For B&W I use either ID11 diluted 1-1 or Rodinal diluted 1-25 and no more otherwise the times become excessively long and with reuse with ID11 even this can become a chore. Rodinal CANNOT be reused!

Even with paper development using Ilford MG, I dilute 1-14 which is permitted even if I only print a couple I always discard at the end of a session, the decay even overnight can result in a reduced quality. It isn't worth it!

With colour RA4 printing because the manufacturers nearly always give a replenishment rate of around 100cc per 800squ ins of paper developed. Different manufacturers may have different rates of replenishment.. This is normal practise with colour which I have found that RA4 has a much longer life anyway part used, especially when using something like a Nova deep tank processor.

 

[Milpool]

Part A of Thornton is basically D-23 slightly diluted. Kodak indicated a shelf life of 6 months for D-23 in a full bottle. Another appropriate comparable is Ilford Perceptol, for which Ilford also indicates a 6 month shelf life (and a capacity of 4 rolls/l if reused).

You might get more capacity out of Thorton part A because part A is poured out of the tank each time before it has done a normal amount of developing.

Will you notice a difference on the 5th roll? Who knows. Will you notice a difference at month 10? Who knows.

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.

 

[Agulliver]

Here's what I do.

I mostly use ID-11 and Microphen, both stock (ie not diluted further). I buy the 1 litre kits due to lack of space. And I keep my 1 litre of stock developer in a plastic concertina bottle, such that as small amounts of developer are wasted (due to imperfect pouring) I can reduce the volume of the container to reduce the air content. This extends the life of the developer a bit.

I count the rolls I develop and have noticed that after about 6-8 rolls I tend to need to add a minute or two to development times. I can usually get 12-15 rolls from one litre. I tend to do 12, then keep that solution to process one 50 foot roll of B&W neg cine film. The latter piece of info probably isn't important, but what is relevant is that real world experience suggests 12 rolls of film can easily be developed with one litre of those developers. I've got as many as 16 rolls out of ID-11 and while I generally use mine up in 2-3 months, it certainly does last about 6 months once made into solution.

 

[dcy]

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.

 

[Alex Benjamin]

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.

With BTTB, the effect of a difference in time will be most felt with bath A.

In bath B, the developer exhausts itself, faster in the highlights and slower in the shadows, so time isn't that much a factor after a certain point.

Worth it reading Thornton's article on this. Was written before Edge of Darkness (the formula isn't exactly the same), but relevant nevertheless.

Barry Thornton articles

Film & silver gelatin darkroom blog covering analogue or analog photography, printing and equipment. Ilford, Kodak, Adox, Olympus, Leica, Rolleiflex.

onlinedarkroom.blogspot.com

 

[snusmumriken]

I'm still thinking about BT2B. Please skip this post if this level of detail seems like getting in the weeds.

This post by @Yezishu in another thread suggests that:
“Assuming a 135 film contains 0.3g of silver, with 25% being developed, this would consume 0.12g of Metol (sulfate).”
Post #41 above in this thread suggests that each film can absorb and carry away 20ml of solution.
I'm not a chemist, and I’ve no idea how realistic those figures are, but at least they provide a starting point for some maths to understand how BT2B ages with successive films.

1 litre of BT2B Bath A contains 6.5g metol. If we assume a worst case where development and carry-over are additive - i.e. that each film first reacts with 0.12g of metol and then carries off 20 ml of the solution - the concentration of metol in the remaining solution would be about 81% after 10 films, 72% after 15 films (see table below). 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.

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.

Because the concentration of metol in Bath A will be falling with successive films, the amount of metol carried in each film emulsion into Bath B to complete development would also decrease by about 25% between film 1 and film 15. 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). At 15 films Bath B would contain about 42% of the metol concentration in Bath A.

Clearly my naïve calculations don’t take into account changes in the concentration of inhibitory bromides, nor of sulphite, nor oxidation of metol in the more alkaline Bath B. Nevertheless it does look as though the way this developer achieves its results may shift somewhat during the life of one developer mix. It makes me think that I should include some test exposures (e.g. zone I, zone IX) on every roll and see how their densities change. That could take me several months, so don’t hold your breath!

 

[Alex Benjamin]

getting in the weeds

Had to look it up.

 

[snusmumriken]

Had to look it up.

@dcy used it in post #52.

 

[Alex Benjamin]

@dcy used it in post #52.

I know. Two people using an expression I had never heard before... bugged the hell out of me.

 

[MattKing]

I know. Two people using an expression I had never heard before... bugged the hell out of me.

For fun, I checked for translations into French - there are lots of possibilities .
The phrase has some crossover similarities with:
"I couldn't see the forest for the trees".

 

[Don_ih]

an expression I had never heard before.

It's more popular and socially acceptable since Trudeau legalized marijuana.

 

[Raghu Kuvempunagar]

“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.

@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. There was a replenisher formula for the first bath which attempted to offset the loss (you can find the replenisher formula through web search in case you're interested) and ensure the same development time throughout the life of Part A.

 

[Yezishu]

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.

A good model! We can assume that x% of development occurs in Bath A, with the remaining (100–x)% in Bath B.
(1) When x = 100, this is the worst-case scenario you described: all development happens in Bath A, so the characteristics of a two-bath process are lost.
(2) When x = 0, the "ideal" two-bath process: Low pH bath A only provide developer to the film, with no chemical reaction taking place. Its volume decreases, but concentration remains constant, allowing use until depleted. The developer carried over with film is then fully consumed in Bath B, whose composition also remains almost stable. The development progress and silver reduction depend mainly on the amount of developer carried over, not on time.
(3) In practice, x likely falls between 0 and 100, with reactions occurring in both baths, for many reasons. The solution composition will change but slower than in (1). Further study would require measuring solution components (e.g., checking if Metol concentration changes match predictions after processing a certain number of films, consider adding some as replenisher and replace Bath B), or, as you said, observing the film for any significant differences in density.

 

[dcy]

@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.

For fun, let me suggest a naive toy model of how development time might increase as Metol gets depleted. Let:

N = # of rolls you have developed so far.
t = Time (in minutes) needed for Part A.

If we write:

t(N) = 4min * 6.48 / (6.48 - 0.12N)

This is a simple asymptotic function intended to diverge to infinity as the Metol in Part A approaches 0.12 --- The denominator is a first order estimate for the amount of Metol left, and I lowered 6.5 to 6.48 so it's divided by 0.12.

t(0) = 4 min
t(11) = 5 min
t(15) = 5.5 min

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.