sodium metaborate in fixers?

What is the purpose of adding sodium metaborate to a simple sodium thiosulfate/ sodium sulfite fixer such as in TF-2?

laverdure said:

What is the purpose of adding sodium metaborate to a simple sodium thiosulfate/ sodium sulfite fixer such as in TF-2?

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It is a very effective buffer at the operating pH and has no negative effects as long as it is of sufficient purity.

PE

PE,
I use the EK fixer F-24. Would there be any advantage to changing to a formula using Sodium Metaborate instead of Sodium Bisulfite?

John, Mount Vernon, Virginia USA

All fixers have good and bad points depending on your needs. The series designed by Bill Troop very adpetly use an idea put forth by Grant Haist in his book.

PE

Photo Engineer said:

It is a very effective buffer at the operating pH and has no negative effects as long as it is of sufficient purity.

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Thanks. But what's the purpose of maintaining a pH in a fixer like TF-2? I assume the buffering is to neutralize any carryover from an acid stop-bath, but I don't know why that would be useful.

An acid stop can be used or a water rinse can be used with the Troop fixers.

Either way, pH must be maintained.

PE

Photo Engineer said:

Either way, pH must be maintained.

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And yet so often people don't bother with the metaborate. A plain sodium thiosulfate fixer with or without sulfite, even measured out by volume in the case of pentahydrate, is a time-honored fix. I've been using Lloyd Erlick's plain fix recipe for both film and paper for some time.

I'm still not clear on the purpose of maintaining the pH of my plain fix. Is it to improve the consistency of fixing time over use?


Thanks again.

There are varying opinions on this. For the Troop formulas, derived from ideas by Haist, it is necessary to maintain the pH at a precise value that borate is able to supply. OTOH, another buffer, acetate is used in acidic fixes, or just plain thiosulfate itself can be used as a buffer if the pH of the fix is selected correctly.

If you want a pH of 10.0 for example, carbonate would be used. If you wish 11 or 12, phosphate would be used, so for every pH value that can be imagined, a given buffer is used. If the pH of a fix goes too high though from lack of stop and too much developer carryover, then the final print or negative can be stained for any number of reasons. Most of these relate to lack of buffering and pH drift.

PE

Anscojohn said:

I use the EK fixer F-24.
Would there be any advantage to changing
to a formula using Sodium Metaborate instead
of Sodium Bisulfite? John,

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Bisulfite and F-24 are acidic. Metaborate is quite
alkaline. With metaborate an alkaline fix. Or, skip
the two and double the sulfite for a fixer
a little alkaline. Dan

Hah, I missed that post. Sorry. Dan is correct.

PE

ll