You would have got that definitely yellow solution *without* any alum,
although alum is supposed to make it more soluble.
Some papers clear a lot quicker than others. I once bought half a ton of
photo grade "raw" paper (no baryta, no emulsion, no nothing) from a major
paper manufacturer. BTW, the minimum order is 22 US tons (45,000 pounds),
so I had to wait for a manufacturer bigger than Atelier Nadeau (there are a
few;-)) to put in their regular order of 22 tons and then the friendly head
chemist would call me and tell me they could make a "little bit extra" for
"experimental" purposes, just for my new Fresson lab... The minimum was one
ton, but I smoothtalked him into half of that... After I put down the
phone, I realized that they would ship this thing in one great big 1,000
pound roll! Another call and he agreed to break it down into "tiny" 200
pound rolls on a 3 inch core. By that point, I knew I had pushed my luck to
the limit:-)
Anyways, photo-grade paper cleared remarkably well with the city water I
was using at that time. High quality thick French papers were a different
story and this was a problem with carbon (single) transfer where the
dichromated pigment tissue was transferred after exposure directly onto the
final high quality paper, which would stain badly. One way around this was
to wash the exposed tissue in *cold* water, in the dark for say, 30
minutes. This does not require (wasteful) continuously running water but
several changes of water. Then it had to be dried thoroughly as a transfer
at that stage would have been impossible on account of the fully swelled
(i.e., no longer adhesive) gelatin. The final transfer, and developing,
could take place days later, in broad daylight, in theory, although I
always found that images got darker the longer I waited for the final
transfer. Obviously, plain water washing of the thick pigmented tissue did
not clear the dichromate residual.
Another way to avoid the stain problem is the double transfer technique.
You transfer to a temporary support, e.g., white opaque plexiglass so you
can monitor what is going on and develop and dry on it. The plexi does not
pick up the stain like paper fibers do. Then you transfer to a final
transfer paper suitable for this technique (it needs a thick, *soft*
gelatin layer) Your final print has no stain whatsoever. You have to be
careful in the various steps so you get an image the right way around.
Finally, for a long time, highly diluted solutions of sulfuric acid have
been used in the photoceramic industry where the dichromate residual
interferes with the firing process. I hate recommending any use of H2SO4
and many schools would no allow it nowadays. HCL, which many Pt printers
may already have at hand would probably do the trick as well.
As to the long term effect of those chemicals on paper and pigmented images
it is nearly impossible to say without intensive accelerated aging tests.
BTW, such tests on my photo-grade paper, mentioned above, made it turn gray
rather quickly. That was fine with me since it has no artistic quality and
all I needed was a cheap paper that costs peanuts per square meter.
Obviously, you want to remove strong acids out of your papers, but when you
look at 500 page thick books on paper fillers, opacifiers, etc., and when
you realize that manufacturers consider their formulas trade secrets, you
quickly face the fact that the variables are into the many thousands...
..
>Also, all of the chemicals so far discussed:
>alum, sodium bisulfite, and sodium metabisulfite are hardeners.
As far as carbon printing (i.e., pigmented gelatin) goes, potassium alum is
a weak hardener. Chrome alum, acidified, is a much more powerful hardener.
The bi and metabisulfites, by themselves, are softeners. There is more on
this in my carbon books.
Luis Nadeau
awef6t@mi.net
nadeaul@nbnet.nb.ca
Fredericton, New Brunswick, Canada
http://www.micronet.fr/~deriencg/nadeau.html
http://www.primenet.com/~dbarto/lnadeau.html#A0