Liam Lawless (lawless@vignette.freeserve.co.uk)
Wed, 26 May 1999 03:25:04 +0100
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
This archive was generated by hypermail 2.0b3 on Thu Oct 28 1999 - 21:39:35