Re: Re : Hypo clear
Richard Knoppow (dickburk@ix.netcom.com)
Thu, 13 Nov 1997 11:06:36 -0800
At 09:59 AM 11/13/97 -0700, Jack Fulton wrote:
>Dave Fokos wrote :
>
>>EDTA is not the main constituent of Kodak Hypo Clearing Agent (HCA),
>>sodium sulfite holds that honor. The other indgredients include: sodium
>>metabisulfite, sodium citrate, and EDTA. Sodium sulfite on it's own is
>>quite a good clearing agent and may be cheaper to use than HCA. I use HCA
>>because of the convenience and effectiveness.
>
>It made me wonder about hypo clearing again after years. i think it was
>Patrick Dignan who first tested hypo clearing products/agents and came
>up w/a recipe which I've lost. But, if memory is correct, he noted that
>the product Hustler was the best in that it was a detergent
>(surfactant). If anyone has info on the 'types' of hypo clearers, I'd
>appreciate it.
>As I understand it there is :
>1. The 1st Kodak one w/Ammonia and Hyrogen Peroxide
>2. The one noted above
>3. Perma wash, which employs both amonium and sodium sulfites
>
>
>While asking questions … could anyone direct me toward info on how to
>make a 'tintype'?
>
>Thanks
>Jack Fulton
>
>
Kodak Hypo Clearing Agent and other so called washing aids are the
result of the discovery that sea water was more effective for washing out
hypo than fresh water. This was first noted around the turn of the century
but extensive research was not until WW-II when the problem of washing
photographic materials on ship board or other locations where fresh water
was in short supply became critical.
It would appear that wash aids work mostly by an ion exchange mechanism.
I've never seen a clear explanation of this so cant provide a citation.
Kodak Wash Aid is approximately: Sodium Sulfite, dessicated, 100 gm; Sodium
Bisulfite, 10 gm; Water 1.0 liter. dilute 1 part stock to 4 parts water
for use. The commercial product will contain the usual chelating agents in
it to deal with hard water.
Kodak HE-1 Hypo Eliminator is works on a different principle. It
converts the residual hypo to Sodium Sulfate which is more soluable. Kodak
has recommended against using hypo eliminator for several years. It can
damage emulsion and may be too effective washing out the hypo. It was
discovered around 1960 that very small residues of hypo actually stabilize
the silver!
I am not sure what advantage Ammonium salt would have over Sodium but
Crabtree et.al of Kodak mentions the use of Ammonium Carbonate as a washing
accelerator in an early paper. It was thought at that time that the main
function of the salt was in changing the pH of the gelatin rather than the
more complex one of ion exchange.
----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com