From: Judy Seigel (jseigel@panix.com)
Date: 12/10/01-12:14:18 AM Z
On Sat, 8 Dec 2001, Sandy King wrote:
> 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
Well, Sandy, you may know that, and I've certainly heard that, but don't
give Scopick any credit for saying so, in or out of the wine. The only
comparative literature on the subject he offers is that Chrome alum has
"tanning action greater than that of ordinary white alum," though as far
as I can see, he never MENTIONS white alum again, ordinary or
extraordinary. Do we have it, know it, use it?
True, the potassium alum entry describes that as "common alum" and says
it's colorless, but never calls it "white." I am considered white, but
definitely not colorless. Is this the way to write a manual?
He also says the potassium (colorless) alum keeps its hardening properties
much better than chrome alum in solution, but gives no criteria for time
or hardening properties in either entry.... which you do below. Thank you.
Did you figure that out yourself or read it somewhere? If the latter,
where?
Finally, if Scopick anywhere gives a formula or instructions for hardening
with either of the alums it is NOT in the index with the alum entry.
As I've said frequently, if I want a puzzle, the NY Times crossword is
better.
PS.: wouldn't you accomplish the semi-hardening just as well by using a
weaker solution?
Judy
> 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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