[pure-silver] Re: Self-Made HypoClear any good?
----- Original Message ----- From: <Camclicker@xxxxxxx> 
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Sunday, November 26, 2006 9:35 AM
Subject: [pure-silver] Re: Self-Made HypoClear any good?
Well, for what it's worth here is the Cookbook formula for HCA: 

quote:
FORMULA #190 Hypo Clearing Agent (HCA)

Water (125 F/52 C)    750.0 ml
Sodium sulfite        200.0 g
*Sodium bisulfite      50.0 g
Water to make            1.0 liter
*The sodium bisulfite lowers the pH in order to prevent softening of emulsion of film. If paper is to be used the bisulfite may be left out in order to 
improve the papers gloss.
end quote
It goes on to suggest double weight paper papers after a 1 minute rinse after fixing needs only a 3 minute HCA bath with agitation and a final running 
water wash of 20 minutes.
I've been using this method for a couple of years and have had no bad 
experiences.


Bruce  Osgood
Camclicker @ aol.com
Brooklyn,  NY.
This is about double the strength of the Kodak stock solution, the formula given by Eric Nelson is about right. If it stays in solution its OK and may have longer shelf life due to the higher concentration but must be diluted more. The working solution is about 2% and has limited life in a tray. It should really be used as a one-shot. The sequestering agents are present to prevent deposition of aluminum from the hardener in hardening fixing baths and minerals from the wash water. They are probably not necessary if the wash aid is used for a small quantity of film or paper but I have not experimented with this. The buffering is used to make the wash aid solution neutral. At neutral the pH of the gelatin is such as to preserve most of the hardening of a white alum hardener while eliminating the mordanting effect. The pH is also such that the electrical charges will repel rather than attract the ions of the fixer and fixer complexes. For much material a simple 2% solution of sulfite seems to work OK. The paper published by Kodak Labs shows the curve of treatment times vs: necessary wash times is asymtotic with a practical maximum treatment time of about 4 minutes. I think Ilford recommended longer times for their "archival wash cycle" because the effect of the wash aid is much less for the support of "fiber" prints than for the emulsion. This is because the hypo is held by mechanical (frictional) forces more than chemical forces once it has soaked into the paper. The ion exchange funtion of the wash aid still help to displace the hypo ions from the paper structure but is not as effective there as it is in the emulsion. Please note that there is no published formula for Kodak Hypo Clearing Agent. If there is a patent I've never seen it cited. The MSDS for both KHCA and Ilford's wash aid are very similar but the exact amounts of anything can not be told from an MSDS and some ingredients may not even be listed. 

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 
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