The suggestion about overexposure is the first & easiest one to check,
but, at risk of sounding like a stuck record, let me note that much of
interest to a new gum printer was discussed on list all last summer & fall.
(Get the list Archive!)
On Sat, 27 Apr 1996, Alan Kleiman wrote:
> Today I started making bicromate gums.
> I sized the paper and coated with gelatin.I used fabriano paper.
Did you harden the gelatine? How long? With what?
> What type of pigment do you recomend.What manufacturing company is
> the best.
Each pigment is sui generis.
> I used watercolor pigment.This pigment was in tube.I don't have a
> scale, so I made the mixtures using ml.The first print was done with a
> dilution of 1ml of pigment and five of gum.Then one part of this solution
> with one part of dicromate.
What color did you use? Pigments are chemicals. Certain ones will harden
in dichromate without exposure.
> The gum solution:
>
> 300g powder gum
> 1000ml of destilled water
> 15 ml of 37%formaldeyde solution
You put 15 ml of formaldehyde in your gum solution? Sounds like a lot to
me. Two drops in 100 ml gum solution have been enough in my experience (10
times two drops would be 20 drops, or one ml for a litre.) But test this
by making some fresh gum solution. It will keep for a day or two with no
preservative and you can see if that's the villain.
>
> The sensitizer formula is:
> 13g of potassium dicromate
> 75ml of water
> This formulas are from THE GUM BICROMATE BOOk DAVID SCOPICK FOCAL PRESS
> ISBN 0-249080073-7
Because you threaten me at gunpoint (gumpoint?) you force me to reveal
that I have tried formulas from this book that did not work.
>
> I exposed two prints, In this case the only diference was the color
> of the print, and that in the print that i exposed 7 minutes, the edges,
> that were not exposed, were removed my the brush.This parts that were
> removed were the parts were the masking was.The pigment from the print, was
> brushed, but no pigment fell off.
Sounds like overexposure then, no?
Gini Boehm said she exposes 30 seconds in direct sunlight.
I expose one minute by blacklight fluorescent, although some gums are
faster than others. A thicker gum I bought from a different supplier is
about 50% faster than my other "regular" gum.
> I really don't know if the problem is that i am not developing
> right, that the expousures are to long, so the emulsion is all harden, that
> i am not using the proper mixture of pigment.
Or maybe all of the above! You'll find some more details in the archive.
Meanwhile, try burnt sienna in fresh gum solution in a test strip in open
shade (direct sun can cook the emulsion entirely, especially in tropical
climes) for one, three and five minutes. Should give you an idea.....
Judy