Gum - what am I doing wrong?

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From: Nash Computer Technology (nashcom@btinternet.com)
Date: 04/06/02-04:02:06 AM Z


Hi

I managed to get some time at Easter to have a bash at gum printing. I had made
some of the chemicals up at Christmas using the formulae in Scopick's book.

I soaked and dried the paper, then brushed on a gelatin/formaldahyde mix and let that
dry.

I mixed 2g of yellow, red and blue pigments (separately) with 10ml of gum.

I then mixed 2ml of the yellow pigment solution with 2ml ammonium dichromate, and
coated this on the paper in dim light, and let it dry in the dark.

I made various test exposures between 1 minute and 1 hour, then soaked the paper in a
number of still water baths. However, there was only the faintest of images, and the
paper didn't clear - the image area stayed a mustard yellow.

I had a think about this, then decided to dilute the pigment solutions. I did a number of
tests by adding an increasing amount of gum to 2 drops of pigment, and brushing onto
some prepared paper then soaking in water to see at what strength the paper cleared.
The yellow started to clear to a magnolia colour at about 2 drops pigment solution to 6
drops additional gum, and going as far as 20 drops gum didn't seem to make much
difference.

I then had another bash at 1 hour exposure, and got a faint image, but the paper still
didn't clear properly.

I had been expecting this process to be quite easy (I thought I might be blessed with
some beginner's luck!), and had been planning on making a tri-colour image. I had a go
with making 3 in-camera exposures with tri-colour red, blue and green filters, and
printing with yellow, magenta, cyan pigments, but I only got a faint image with a muddy
brown background.

By the way, I shot the images on Tri-X rated at 100ISO and developed in Rollo Pyro for
about 4 minutes (about half the time I normally use for platinum).

Any help would be much appreciated.

David Nash


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