[alt-photo] Re: Sulfite + Na4.EDTA clearing bath quick kitchenformula?

[Richard Knoppow]

----- Original Message ----- 
From: "Loris Medici" <mail at loris.medici.name>
To: "The alternative photographic processes mailing list" 
<alt-photo-process-list at lists.altphotolist.org>
Sent: Friday, February 24, 2012 12:29 PM
Subject: [alt-photo] Re: Sulfite + Na4.EDTA clearing bath 
quick kitchenformula?


> Same here...
>
> OTOH, I'm not sure I'd like to include citric acid into 
> Na4.EDTA; I
> already do process in citric acid first, and would prefer 
> to leave the
> paper in a neutral/alkali condition for best possible 
> longevity.
> Still, I may use it as the first clearing bath and then do 
> another
> clearing run w/o the citric acid, in case of stubborn 
> papers that
> won't clear the first time...
>
> Thanks again,
> Loris.

     I am curious because the clearing bath sounds a lot 
like Kodak Hypo Clearing Agent although the purposes are 
probably different. KHCA is a mixture of sodium sulfite and 
sodium metabisulfite to obtain a buffer with a pH of 7. It 
also contains a small amount of EDTA tetrasodium salt and 
some sodium citrate. The sodium citrate is not acetic acid 
but is evidently like it e.g, a sequestering agent. The 
purpose of the sequestering agents in KHCA are to prevent 
deposits of aluminum compounds from paper and film hardened 
with white alum and to prevent deposits of carbonates from 
the water. The stock solution is about 10% sulfite and is 
diluted to about 2% for use as a hypo remover.

--
Richard Knoppow
Los Angeles, CA, USA
dickburk at ix.netcom.com