Why the time differences between Ilford and Kodak rapid fixers?

Doremus Scudder · 07-02-2009, 01:29 PM

I always assumed that the Ilford and Kodak rapid fixers were similar products. I've noticed recently, however, that there is a rather significant discrepancy in the recommended fixing times for fiber-base papers.

Ilford's recommendation (from the pdf document from the Ilford web site) for "film-strength" rapid fix (1+4) is 1 minute; for "paper strength" (1+9) is 2 minutes. For two-bath fixing they recommend half the respective fixing time in each bath.

Kodak's recommendation for fiber-base papers (from the instruction sheet packed with the product) are longer: 6-10 minutes for single bath at "paper strength" (1+7) and no recommendation for "film strength."

Given that the recommended times for "general purpose films" are almost exactly the same (2-5 minutes for Ilford, 2-4 minutes for Kodak), I would assume that the respective dilutions of the products were similar.

Why, then, does Kodak indicate triple the Ilford recommended time as a minimum for fiber-base paper? Are Ilford times too short? Is Kodak being over-cautious? Are the fixers really different? What gives?

TIA

Doremus Scudder
www.DoremusScudder

Ian Grant · 07-02-2009, 01:43 PM

They are quite different formulae, the Kodak product contains a hardener, and works at pH 4.4 while Hypam/Ilford Rapid Fixer has a pH of 5.4 (working solution).

The hardener & more acidic pH will slow fixation, and also mean longer wash times are needed. Hypam differs very slightly from Ilford Rapid Fixer in it's buffering which allows a hardener to be used if needed, but otherwise they are interchangeable.

Ian

clayne · 07-02-2009, 01:46 PM

Pretty sure the Kodak RF does not include a hardener. Their normal fixer does include a hardener, however.

Ian Grant · 07-02-2009, 01:50 PM

Kodak's MSDS indicates Aluminium Sulphate and Sulphuric acid in Kodak Rapid fixer, they are only used for hardening, and to acidify the Fixer to pH 4.4 which is necessary to keep the Aluminium Sulphate in solution.

Ian

Photo Engineer · 07-02-2009, 01:55 PM

I have tested both Kodak and Ilford papers in Kodak fixers and some of my own formulation. I find that the Kodak papers (now defunct) fix more slowly than the comparable Ilford papers. So, the difference in instructions may also reflect a carryover from this observation. Kodak probably established that data using their own Polycontrast Rapid IV years ago.

However, presence of a hardener will slow fixing and washing. Also, pH would affect fixing slowing it as pH goes down, so this may also be a factor even if hardener is lacking.

PE

Paul Sorensen · 07-02-2009, 01:57 PM

Kodak rapid fixer comes in two parts, one is a hardener. I have always used it without, but it is there for those who want to use it. I am guessing that the MSDS is for the solution as used, so it would include the hardener. You can see this on this page at Freestyle.

clayne · 07-02-2009, 02:03 PM

I stand corrected, then. :-)

Ian Grant · 07-02-2009, 02:07 PM

It's worth noting that in some thread hear on APUG people mention leaving out Part B of Kodak Rapid fixer, this is the Hardener, as it only contains the Sulphuric Acid and Aluminium Sulphate you effectively have a Fixer very similar to Hypam.

One reason many Pyro users want Alkaline fixers may well have do with the Sulphuric acid in Koadak Rapid Fixer.

Paul the MSDS is for Part A, Part B and also the working solution.

Ian

john_s · 07-02-2009, 05:48 PM

During the controversy about Ilford's rapid FB print washing technique, in which fixing is done, I think, with film-strength fixer for a very short time in order to prevent fixer from penetrating the paper base much, it was said by various people that the technique does not work with some brands of paper incl Kodak, because they need longer fixing. I don't have any references, sorry, because I never liked the idea of fast fixing. And I used some non-Ilford papers.

dancqu · 07-02-2009, 06:37 PM

Quote:

Originally Posted by Doremus Scudder

Kodak's recommendation for fiber-base papers (from the instruction
sheet packed with the product) are longer: 6-10 minutes for single
bath at "paper strength" (1+7) and no recommendation
for "film strength."

Doremus Scudder www.DoremusScudder

I think it must have been faster 50 years ago when I switched
to Rapid. Now days I'm back to Slow, in more ways than one.

The one minute fix in film strength is an Ilford invention. That
one minute fix is followed by a 5-10-5 high intensity wash-
hca-wash. The one minute fix and following wash routine
are the quickest way to a well fixed and washed print.
No more than that IMO.

Those times, BTW, do they stand for the last print through
a fixer at it's limits of capacity? Dan