[pure-silver] Re: ARISTA-EDU Ultra 100iso
- From: Gerald Koch <gerald.koch@xxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Fri, 23 Dec 2011 11:37:03 -0800 (PST)
Potassium chromium sulfate (chrome alum) is sort of a neat chemical. It
exhibits dichroism, its solution appears purple by reflected light and green by
transmited light. Years ago when people weren't taught to fear all chemicals
it
was included in kits for children to grow large crystals.
Jerry
________________________________
From: Richard Knoppow <dickburk@xxxxxxxxxxxxx>
To: pure-silver@xxxxxxxxxxxxx
Sent: Fri, December 23, 2011 11:35:31 AM
Subject: [pure-silver] Re: ARISTA-EDU Ultra 100iso
----- 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
=============================================================================================================
To unsubscribe from this list, go to www.freelists.org and logon to your
account
(the same e-mail address and password you set-up when you subscribed,) and
unsubscribe from there.
Other related posts:
