This is weird - Ilford rapid fixer

[tkamiya]

I'm going over the documenation for Ilford Rapid Fixer.

http://www.ilfordphoto.com/Webfiles/2006130218312091.pdf

On page 2 of 5, there is a chart for "capacity without replenishment" that lists expected life of fixer in different dilutions per liter of working strength solution.

Looking at RC paper for example says for both 1+4 and 1+9, it is capable of processing 80 sheets PER LITER of working solution.

How could this be? 1+4 and 1+9 have different amount of active ingredients per liter in it. Being fully aware higher dilution takes longer to process, it is basically telling me, by going 1+9 I can process twice the number of paper than going 1+4....

A 500cc bottle makes 2500cc working solution at 1+4 that can process 200 sheets (80 sheets per 1000cc working strength solution)

A 500cc bottle makes 5000cc working solution at 1+9 that can process 400 sheets
(80 sheets per 1000cc working strength solution)

Am I reading this right? Weird....

 

[Rick A]

Umm... How about because they both use the same amount of fixer. The only difference would be time spent in the fixer.

 

[tkamiya]

Hi, Rick...

Wouldn't you think it's weird though, I can get better sheets-processed economy by diluting it as twice as much? Regardless of how long it takes to process it, active ingredients should be used up at the same rate and contamination increased at the same rate per paper processed.... me thinks?

 

[lns]

You must fix it twice as long at the higher dilution.

-Laura

 

[MattKing]

Don't forget that with fixer, capacity is determined in part by how much silver has been deposited into solution as part of the process. It may be that the amount of silver in solution is the limiting factor, rather than the quantity of active ingredient remaining.

 

[CBG]

I'm betting on that being an error. I think the more concentrated solution should have greater capacity.

 

[tkamiya]

This is STILL weird. I'm sure this math doesn't scale forever but I wonder if I dilute it 1+19, I get to fix 4 times number of prints if I am willing to soak it for 4 times longer?? Granted this is no longer "Rapid" fix but very economical...

 

[tkamiya]

It'd be very nice if Simon can say for certain if this is a misprint on spec sheet or if Ilford rapid fixer rally works this way. I was thinking more concentrated the solution, shorter fix time (which is stated so in the spec sheet) but number of sheets processed per given amount of concentrated solution being constant - meaning higher dilution having less capacity per liter. (which isn't the case per spec sheet and hence my wonderment)

 

[MattKing]

I quote from the fact sheet you referenced:

"Capacity without replenishment
An unreplenished fixer bath is eventually
exhausted by the build up of silver and halides in
it and the action of solutions carried over from the
preceding baths that can cause some dilution and
the pH to be raised."

(my emphasis added)

No matter what the dilution, 80 sheets of paper will still cause the same build up of silver and halides in the liter of working solution.

 

[Simon R Galley]

I will have it checked out and come back to you.

Simon ILFORD Photo / HARMAN technology Limited :

 

[Thomas Bertilsson]

This makes complete sense to me. I don't think it's a misprint either.

I quote from the fact sheet you referenced:

"Capacity without replenishment
An unreplenished fixer bath is eventually
exhausted by the build up of silver and halides in
it and the action of solutions carried over from the
preceding baths that can cause some dilution and
the pH to be raised."

(my emphasis added)

No matter what the dilution, 80 sheets of paper will still cause the same build up of silver and halides in the liter of working solution.

 

[Simon R Galley]

Dear Thomas et al,

I have spoken with our tech service and the statement is correct and consistent with the published TI sheet on HYPAM as well. They say " Firstly, in terms of paper / film throughput we will always be fractionally on the safe side so as to protect the customer. The reason the throughput is the same although the dilutions are different is purely because there will always be a maximum known quantity of paper or film which will generate build ups of silver(s) and a pH change to the point which we measure, and therefore classify, as being 'near' exhaustion / exhausted. It is the actual meterage that causes this, regardless of the strength of the fixer, it is not possible 100% to say the actual throughput exhaustion levels are exactly the same for both dilutions but it is as near as makes no material difference. Please remember if using the higher dilution of 1+9 to double the fix time".

Regards

Simon ILFORD Photo / HARMAN technology Limited :

 

[tkamiya]

Simon,

I'm the OP on this thread. Thank you VERY MUCH for your official reply. I wanted to make sure I understood the tech spec correctly before mixing up my first batch of Ilford Rapid Fixer. I feel good about using it now.

Taka

 

[hrst]

Probably if it were to be diluted even further, then the capacity would start to drop because the remaining thiosulphate (active agent) level would become a restricting factor in addition to (or instead of) the concentration of silver thiosulphate complexes and halides (Br, I) (reaction products).

Or to rephrase, the fixer is very "strong" to begin with so you can use higher dilution to save costs, until a certain point when it becomes too dilute. Then the capacity probably starts dropping quite linearly and you won't save anymore, just lose time.

Well, there may be some difference in capacity even with those dilutions, more strong having a bit higher capacity, but it may not be relevant enough to show in instructions. After all, it all depends on films used (different films have different amounts of silver and iodide), and also the exposure and scene content - overexposure or bright scenes can save some fixer!

 

[CBG]

Very interesting. Thank you Simon for responding and making sense of that.