Re: How to super harden papers?

From: Sandy King <sanking@clemson.edu>
Subject: How to super harden papers?
Date: Tue, 22 Mar 2005 08:43:43 -0500

> bottle of the potassium alum hardener that comes with Kodak Rapid-Fix.

Potassium alum has a relatively narrow pH window in which hardening
effect can be usable. Generally, you want to use highest pH without
sludge formation for maximum effect. With boric acid in the bath, this
can be as high as 6, but if you are interested in pursuing this route
before the next step, I'll try to pull papers to check.

> My thinking is that the gelatin might harden more with the addition
> of some formalin or glyoxal to the fixer. Does anyone know if this
> might work, and if so, have a general guide as to how much to add per
> liter of fixer?

I don't recommend addition of glyoxal or formaldehyde in fixing bath.
If they are used as a hardener, I instead recommend a separate
hardening bath in a very well ventilated area. The easiest-to-use and
most effective hardener in this category is glutaraldehyde, which
hardens fast and also in a widest pH window.

The reasons I don't recommend to mix them in fixer are: (1) they can
react with sulfite in the fixer, (2) useful life may be limited by the
fixer exhaustion, (3) the condition of hardener use may be more
restricted (in darkroom, for example, when fixing light sensitive
material).

Glutaraldehyde hardening bath was a standard step in older color
reversal film processing (see Forst 1972, US Patent 3634081). There
Ektachrome 2448 is hardened in 2% glut solution containing 10% sodium
sulfate for 30 seconds at 38C after stop bath. You can use more dilute
solution at room temperature by giving longer treatment time. (2%
solution in an open tray will make plenty of irritating fume, so I
recommend to use good ventilation, and also cover the tray before,
during and after the treatment of each print.)

If you prefer formaldehyde bath, Kodak SH-1 formula is published: 10ml
of 37% formaldehyde (commercial formalin) and 6g sodium carbonate
monohydrate with water to make one liter. This one will give at least
as much irritating fume than glut and same warning applies.

Glut hardener can be used before development, after stop bath, or
after fixation. Generally the same applies to other aldehyde hardening
baths, but they may increase the fog level if used with silver-gelatin
material before development. If formaldehyde needs to be used before
development, formula like SH-5 is recommended to reduce this problem.

I might repeat that a liter of 2-4% glut or formaldehyde in an open
tray is a lot more than what I'm willing to use in my darkroom at a
time. This is the kind of quantity sometimes used by health care
professionals in hospitals (cold sterilization applied to instruments
that cannot be autoclaved). You might find a tightly sealable
tupperware or something to keep the solution and perform the
processing, instead of ordinary processing trays. Anyway, mental
simulation of the entire processing line with potential disaster in
mind is in order before doing any of these stuff.

--
Ryuji Suzuki
"Well, believing is all right, just don't let the wrong people know
what it's all about." (Bob Dylan, Need a Woman, 1982)