How to formulate a replenisher -- standard guidance?

I was reading, in a separate post, a comment provided by Ian Grant about D-76 and its replenisher -- Ian provided the formula for both. IIRC, the replenisher had more hydroquinone than D-76, and significantly more borax.

That got me wondering if there's a general "rule" for formulating replenishers? I'm curious because I've been using an MQ formula found in the "Darkroom" book, and I've tried replenishing it by simply replacing a specific quantity with the regular formula, but I wonder if I shouldn't be using a different "mix" for the replenisher.

Any thoughts -- from Ian or anyone else -- on formulating developers?

I'm afraid someone is going to tell me that I actually have to do a chemical analysis of which chemicals get depleted in development, which will be beyond my 1969 high school chemistry skills!

There's an article on replenishers published in the BJP Almanac in the 1950's. It's was part of a series of research documents.

Essentially Ilford tested how developing agents were depleted by development and how bromide & iodide build up impacted the replenished developer. This was during the evaluation & design of a PQ replacement for D76 for photofinishing.

There's two types of replenishment, bleed where a fixed amount of replenisher is added per sq meter of film processed, some developer must be bled off first to allow the volume to stay constant, that's how D76 is replenished. This is to keep the level of by products like iodide & bromide leached from the film low.

Topping up replenishment just adds what's used and carried over to keep the volume constant, Ilfoprd's PQ photofinishing dev Autophen could be used that way, Metol is highly susceptible to iodide & bromide build up, phenidone isn't. Colour processors use the top up system.

A PQ version of D76 can be replenished virtually ad-infinitum while D76 needs dumping every 6 months or so, depending on throughput.

So you can calculate the extra developer you need to add, and from testing the ph show what additional buffering is needed, you'll see that replenisher never has any bromide even when it's used in the developer.

That's the simple answer

In practice Ilford did extensive lab testing and with commercial photo labs on a larger scale before finally releasing Autophen.

Ian

Thanks, Ian. That's very helpful. I had in fact been doing a bleed replenishment, but I was only swapping out maybe an ounce (US) from a half gallon (IIRC), and that probably wasn't enough to get done what needed to be done. I'll try about 3 ounces next time.

D-76 Replenisher!

Has anyone out there tried using Freestyle L Pro D-76 Replenisher with Kodak D-76 Developer, straight? Freestyle can not tell me if the two are compatible!
Thanks!!

Mason discusses replenishment in detail along with how to calculate the composition of a replenisher.