Richard Knoppow (dickburk@ix.netcom.com)
Tue, 25 May 1999 21:33:47 -0700
At 03:25 AM 5/26/99 +0100, you wrote:
>Hi Judy & Everyone,
>
>Don't like to disagree in public, but I haven't come across the point you
>make about "used fix", and came to the conclusion a long time ago that the
>term "fresh fixer" is not meant to be taken literally, but means a fixer
>that is not at, or close to, exhaustion. A stupid thing to say as there are
>few occasions when we'd want to use an exhausted one (except, perhaps, for
>making hypo-alum!), but if we used "fresh fix" every time fresh fix is
>specified, we'd all use a great deal more fixer.
>
>My understanding of how it works is that (as I said earlier) an insoluble
>silver-thiosulphate compound forms at first (which is what does not wash
>out), and this becomes soluble not merely in an excess of free hypo, but in
>a SUFFICIENT excess of free hypo. The amount of silver that a fixer can
>dissolve is not wholly determined by the amount of hypo it contains (cf. the
>solubilities of different chemicals), hence there is an "optimum" amount of
>hypo which I believe is about 250g of the crystalline form per litre. But
>the solution becomes saturated with silver long before all the hypo is used
>up, at which point any more silver no longer becomes completely soluble, and
>so remains in the film/paper, even though "spare" hypo is still present.
>This is what must be avoided, and, I believe, is what "fresh fix" refers to.
>
>I also believe that poorly-fixed prints can be saved by re-fixing properly
>at a later date (just as stabilised prints can be made archival by proper
>fixing and washing), providing they are caught in time - i.e. before
>staining has occurred. (But maybe I'm wrong about this?)
>
>Was finally getting some printing done and someone had to send a message,
>didn't they??
>
>
>
>Liam
>
>
>
AFAIK this is correct. As long as the print has not started to sulfide it
can be re-fixed in fresh hypo and re washed.
It turns out the capacity of a single fixer bath is surprizingly limited.
The use of two bath fixing insures that the complexes in the emulsion are
water suluable and extends the usful life of the baths considerably. Both
Kodak and Ilford have published reams of stuff about this.
The capacity of a single fixing bath for archival fixing as given by
Ilford is only about five to ten 8x10 prints per liter. This is extended to
about 40 8x10's when a two bath system is used.
Film emulsions are more rugged than printing paper but still should be
fixed using the two-bath system.
----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com
This archive was generated by hypermail 2.0b3 on Thu Oct 28 1999 - 21:39:35