I bookmarked your post. Thank you for this! Do you mind sharing, on a high level, how did you do these calculations? Is there a common variable in Kodak's Z-131 and Fuji data sheets that allows to infer the starter-to-replenisher ratio?
Hi, and you're welcome.
Re the calcs... as I said it's a very roundabout way. I should probably mention that I've had a very substantial amount of experience with the standard color neg/print processes, including regeneration of everything that was feasible. This included use of a decently equipped chem lab. So I know what sort of things to look at.
I was gonna try to make this simpler, but to be understandable I think the background information has to be available. The last paragraph is the summary, more or less, if you understand what it means. Sorry it's not easier to follow. People who have written technical reports know that it's a lot of work to edit something down to a short and sweet, and understandable version. I just left this in the long tedious form.
Ok, the main things that slow down C-41development are byproducts released when development occurs. Of these, the easiest to look at is probably bromide ion in the developer. It is released in nearly exact proportion to the physical amount of silver developed. It is not commonly known how much bromide should be in the developer, but this was publicly revealed by Grant Haist in his book, Modern Photographic Processing (vol 2) as the "C-42" process formula. All C-41 developers are fundamentally the same in this respect - only the replenishers are different. They will typically contain some bromide of their own (as NaBr, I think), where only the lowest replenishment rate system can have zero NaBr. As a note it is not possible to have a lower rate replenisher as there must be enough physical volume to dilute the released (by development) bromide (expressed as NaBr) back down to the aim spec (per Haist). Likewise, any higher rate replenisher must already contain SOME amount of NaBr, else it would over-dilute the bromide in the working developer tank solution. I know it may sound terribly complicated, but it's not really. If the terms bromide or NaBr make it seem difficult, just pretend that they are something you are more familiar with, maybe "dirt" or "purple food coloring," for example.
Ok, how I calculated, roughly, the starter requirements. I forgot to mention that a main purpose of the starter solution is to add the appropriate amount of bromide to the replenisher, in order to make it into a proper working tank solution. There is one other thing that must also happen. The replenisher must necessarily have a higher concentration of the actual developing agent, CD-4 in this case, so the replenisher must always be somewhat diluted when converting it into working tank solution. Just fwiw.
Ok, finally, my general method. This is gonna be hard to follow, as it's not straightforward. No big deal, as it's not that important - just an exercise "to see." (As a note, I originally did this, as I recall, to see if a regular person, without inside information, could calculate this sort of thing.) First I estimated how much bromide is released by the "average" roll of film. So very roughly the average amount of bromide released by developing film is just enough to bring the added replenisher to the aim spec for NaBr. Kodak specs the replenishment rate for LORR replenisher at around 20 ml/roll, 135-24. So the average roll developed releases enough bromide (expressed as NaBr) to bring that 20 ml up to the Haist aim spec. If you see the LORR replenisher as having zero NaBr in it, then you can estimate the amount released by the film. Given the amount released by the film, you can look at other replenishers, operating at higher replenishment rates, and estimate how much NaBr those replenishers already contain. Then, if you look at Kodak data for making a fresh working tank solution, using Kodak starter solution, you can calculate an estimation of the NaBr concentration in the starter.
All this gives you enough info, more or less, to work out roughly how much LORR starter to use in another line of replenishers, given only the replenishment rate for it. From the replenishment rate you can estimate the NaBr concentration already in the replenisher. Knowing that, plus knowing the NaBr concentration in the LORR starter, you can calculate how much starter is needed, more or less. One added complication in the works is the water dilution. So the combined water plus starter plus replenisher have to total up to reach the aim spec for a working tank solution. Regarding the water dilution, I truly don't recall exactly how I got to that. I think I may have have just made up a number midway in other starter instructions, where the differences were relatively insignificant. (To do it more properly you could probably work out CD-4 numbers in a similar manner.)
Let me know if I can clarify any of the confusing parts.