From: Sandy King (sanking@clemson.edu)
Date: 12/08/01-02:57:10 PM Z
Judy Seigel wrote:
>On Sat, 8 Dec 2001, Ted Edkins wrote:
>
>> Judy, I stand admonished for mentioning "that" book and writer. A good
>> example of what you say is that I wrote the mail from home and when I got
>> to work I looked up my chemical catalogues and found that chrome alum is
>> not usually sold as the dihydrate but as the dodecahydrate ie not 2H20 byt
>> 12H2O. This makes you wonder about other typos and mistakes. I promise
>> never to mention that work again.
>> Ted
> >
>
>Ted, you are obviously a gentleman & a scholar... now if you can come
>up with a test for glyoxal...
>
Well, that aside I am going to be a fly in the wine. Regardless of
whether Scopcick discovered the fact, or repeated something said by
someone else (most likely), the fact of the matter is that chrome
alum (potassium chromium sulfate) does harden better than potassium
alum (potassium aluminum sulfate), or at least in equal amounts it
does the job much faster. I mentioned some days ago that I use both
chrome alum and potassium alum in preparing final support papers for
carbon, the former for single transfer papers that have to be well
hardened because they will be used to develop the image in hot water,
and potassium alum for the final support paper for double transfer,
because for this I need a gelatin that is only semi-hardened. I use
the same amount of both of the alums for a given quantity of gelatin
solution, about 2-3g per 1000ml of solution. If you test for
hardening after several days by placing papers prepared with the two
hardeners in a tray of water at about 75F, the gelatin surface of the
paper hardened in chrome alum remains very hard, while the paper
hardened will swell a lot and become almost slimy to the touch. Even
after 6 months to a year the paper hardened in potassium alum will
retain this ability to swell and become slimy to the touch.
It would be difficult to confuse the two alums. Chrome alum looks
like final particles of purple sand, potassium alum almost like sugar.
Sandy King
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