Re: chrome alum

[Sandy King <sanking@clemson.edu>]

Title: Re: chrome alum

Chris wrote:

>      
> Sandy King (or anyone else in the know), a while back you said you
> usually use chrome alum for hardener, sometimes potassium alum, too. 
> You
> mentioned mixing 2 g of chrome alum (the purple stuff)  per 1000
> ml of
> gelatin solution.  This is about 1/2 tsp.  How much
> *gelatin* do you use in
> your 1000 ml--my formula calls for 2 tsp Knox gelatin, does yours,
> too?
>      I'm starting to work with tiles and glass to
> get liquid emulsion to
> stick, and a student wants to try to sub glass with the chrome alum
> solution
> for gum; she tried it already with varnish and a mild sanding and the
> gum
> totally came off.  She was inspired by my telling her a while
> back about
> Sarah Van Keuren's students doing gum on glass. Short of a
> sandblaster,
> we're going to keep trying.
> Chris

Others have already addressed part of your message about chrome alum, but not as I recall the part about how much gelatin should be used per 1000ml of solution.

First, a couple of points. My use is almost certainly different from yours as I size paper to serve as final supports for carbon transfer prints, not for gum printing. Second, as Don Bryant's copy of part of a previous message I posted to the list on this topic indicates, I size differently depending on whether I am working with the single or double transfer method in carbon printing.

For my single transfer papers, which would probably work well for gum printing as well, I use about a 3% gelatin solution, that is, about 30g of gelatin dissolved in 1000ml of water. To this I add 2-3g of chrome alum, which I first dissolve in about 50ml of warm water. I often also add a few grams of corn starch to the sizing solution, the purpose of which is to give a more matte look to the borders of the final print.

I coat with this sequence:

1. Soak the paper in warm water for about 10 minutes.

2. Squeegee the paper to a flat level surface.

3. Wipe off the excess water with a clean towel.

4. Apply the coating with a brush, allowing about 100ml of solution per 22X29" sheet of paper. If air bubbles form during coating, mist with alcohol.

5. Allow the gelatin to set.

6. Dry by either hanging from a line or by placing on a drying rack.

One coating usually suffices for my application but very thick and rough paper may require an additional layer of sizing.

One could substitute 2-3ml of either formaline or glyoxal in place of the chrome alum. I don't use formaline because my coating is done indoors and the fumes are impossible to live with and don't use glyoxal because it yellows my papers. Papers sized with chrome alum should be set aside for several days before use because the hardening takes longer than with formaline and glyoxal.

Sandy King

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