Quick TF-5 Question

[andwood]

I've just ordered some TF-5 in a liter bottle for my new at-home setup for film processing (using up some HC-110 for developer and want to try out Pyro when that runs out). I got a Jobo setup with the manual roller and in looking at the tank, they only need about 470ml of chemistry for the rotary process (1540 tank). I think that rounding up to 500ml would be easier measurement-wise, so I would be putting together 125ml of TF-5 and 375ml of water for 500ml working solution.

My question comes about in the instructions where it states "For film the capacity is 15-20 rolls of film per liter of working solution." Would this amount at 500ml of working solution still do 15-20 rolls? Or if the working solution is smaller than a liter, would it have a different roll yield? My logic would say yes if it is used in a timely fashion, but I wanted to double check as chemistry was never my strength. Thanks!

 

[MattKing]

Welcome to Photrio.
If the capacity is 15-20 rolls per litre of working solution, then that means that the capacity is 7.5-10 rolls per half litre of working solution.
But if it were me, I would make up a litre at a time, and just use whatever you need for your tank for each processing round, with the recently used fixer being poured back into the bottle each time. Then after 15-20 rolls, you can set the used up fixer aside for recycling.
And I would check that capacity by also doing regular clearing time clip tests. As some films - e.g. the T-Max films - exhaust fixer more than others, those capacity recommendations are best treated as guides.
Here is a reference article I put together which explains how to do a clip test. You can decide if the rest of my routine makes sense for you: https://www.photrio.com/forum/resou...ixing-procedure-for-black-white-negatives.75/

 

[andwood]

Awesome, I appreciate your help. I was used to a very specific process in a community darkroom so jumping into rotary and doing this at home have taken a few moments to conceptualize in my head. I'll go with the liter working solution with the 15-20 rolls and check regularly. And great point on the T-Max, I'm ending a bulk roll of 100 now that gave me some problems fixing in the past (well, I gave it problems by not fixing it long enough).

 

[Doremus Scudder]

Matt has your answer. Doing clearing-time tests is much more accurate than using throughput recommendations. Don't hesitate to discard the fixer even when it's getting close to exhaustion. Fixer is cheap, film isn't.

Just FYI, fixer exhaustion is a rather complicated things. It's not just that the fixer chemical gets used up gradually, but also the fixing reaction gets slowed down by the build-up of fixing by-products. When these reach a certain point (2x clearing time in fresh fix!), the fixing is no longer complete. So, you can see that the point of exhaustion depends on the total volume of the fixing bath being used, not so much on the dilution (by-products build up at the same rate regardless of dilution).

TF-5 is a great product, but make sure you stop development completely with either an acid stop or several changes of water rinse in your Jobo. Carried-over developer can be re-activated in an alkaline fixer and cause fogging and streaking, so don't skimp on the stop-bath step.

Best,

Doremus