Re: Clearing Gum Bichromates
s carl king (sanking@hubcap.clemson.edu)
Fri, 12 Jan 1996 13:00:59 -0500 (EST)
>
> >On Thu, 11 Jan 1996, Luis Nadeau wrote
> >
> >We use the double transfer technique in our 3-color carbon process. When we
>
> I'm not following you here. Of course, the double transfer mentioned above,
>
> This is the method I preferred (until I ran out of hair to pull out;-))
>
>
dont remember seeing any dichromate at that stage on it. (How about you
> Sandy?) The image and its final support get another few minutes of hot
>
No, I too was very confused as to what Hans meant in his statement
about a dichromate stain on the STS. I presumed he was talking about
three-color work of the type you describe. I follow procedures
very similar to yours in working three-color carbon and carbro and
have never seen even the slightest hint of a stain on the STP. When
the color reliefs are developed on plastic the image develops
absolutely clear, with no trace of dichromate, at least this is the
case with the temporary plastic carriers I use (a polyester product
called Kal-glas).
>
As for clearing the bichromate from paper, I use sodium bisulfite. However,
my practice is to first dry the carbon/carbro image first and let
it stay aside for a few days for the gelatin to harden before clearing.
You risk ruining the image by clearing while still wet with either
sodium bisulfite or potassium metabisulfite (and is there another
-sulfite I forget) because they soften the gelatin somewhat and it
is already in a very softened state, especially with carbro.
(I am of course talking about monochrome printing now.)
Another thing I have observed is that you must renew sodium bisulfite
on a regular basis. If old or exhausted sodium bisulfite is used
to clear papers it will stain the paper blue. This has happened to me
with both Fabriano and Rives papers hardened with chrome alum, and
I believe (though not positive) also with formalin.
Sandy King
Sanking@hubcap.clemson.edu