Re: Clearing Gum Bichromates

Luis Nadeau (nadeaul@darwin.nbnet.nb.ca)
Fri, 12 Jan 1996 17:04:14 -0400

> 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).

There you go Hans. The Masters have spoken;-) What is your procedure?

>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

This is why in a previous post I mentioned that they were not hardeners.

>(and is there another
>-sulfite I forget) because they soften the gelatin somewhat and it

it would have to be ammonium I guess.

>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

That is new to me. Never heard tell of that. It must take quite sometime
before it gets to that point?

>with both Fabriano and Rives papers hardened with chrome alum, and
>I believe (though not positive) also with formalin.

Luis

>Sandy King
>Sanking@hubcap.clemson.edu