[pure-silver] Re: ARISTA-EDU Ultra 100iso
- From: "KISS BOB" <bobkiss@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Sat, 24 Dec 2011 12:23:49 -0400
DEAR RICHARD,
When I first moved to the tropics I researched a few
"warm temp" formulae. Some recommended that the addition
of sodium sulfate alone hardened the emulsion. Is the
SB-5 you posted below considered a hardening stop bath?
MERRY HO-HOs & HAPPY NEW-NEWs!
On Fri, 23 Dec 2011 08:35:31 -0800
"Richard Knoppow" <dickburk@xxxxxxxxxxxxx> wrote:
----- Original Message ----- From: "Howard Efner"
<hfefner@xxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Thursday, December 22, 2011 7:48 PM
Subject: [pure-silver] Re: ARISTA-EDU Ultra 100iso
Chrome alum (potassium chromium sulfate) will harden
gelatin rapidly - in a couple of minutes. It does have
the problem of streaking and throwing down chromium
sludges when it becomes exhausted. It is the chemical
specified in hardening stop baths.
Potassium alum ( white alum or potassium aluminum
sulfate) will also harden gelatin, but its action is
slower. About 24 hours is required for potassium alum to
harden a gelatin sizing. It is also used as the
hardener in acid fixers. Again, time is required to
achieve maximum hardening. It is also pH dependent -
likes mild acid conditions to be effective.
Howard Efner
J.D.Beyer is correct about SB-4, it is a chrome alum
stop bath and hardener, once recommended for tropical
processing of film. It can leave a stain so was never
used for paper. Chrome alum is quite acidic by itself so
it makes a good stop bath with nothing else. It also does
not bind hypo or its reaction products as white alum
does. It is as you state a much more effective hardener
than white alum. Its slightly purple when fresh but turns
yellow-green when becoming exhausted. When it turns color
it can leave stains.
Potassium aluminum alum is the conventional white
alum used in fixing baths. The reason that old fixing
instructions specified such long fixing times was mostly
to allow the hardener to work.
Steve Anchell may have confounded SB-4 with SB-5
which contains sulfate:
Kodak SB-5 General Purpose Stop Bath for Films and
Plates
Acetic acid, 28% 500.0 ml
Sodium sulfate, desiccated 45.0 grams
Water to make 1.0 liter
If crystalline sulfate is used increase the amount by
1.5X
Allow the film to remain in the bath for about 3 minutes
before transferring to the fixing bath.
While Anchell's book is a good resource it is,
unfortunately, _not_ reliable.
My source is the Kodak publication _Processing and
Formulas_ from the Kodak Photographic Handbook_ 1948
edition.
This film sounds more like a 1930s than a 1950s
emulsion.
--
Richard Knoppow
Los Angeles
WB6KBL
dickburk@xxxxxxxxxxxxx
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