Re: Gum - what am I doing wrong?

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From: Hamish Stewart (hamish@gumphoto.fsnet.co.uk)
Date: 04/09/02-01:27:40 AM Z


On 6/4/02 10:02, "Nash Computer Technology" <nashcom@btinternet.com> wrote:

> 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.

David you don't mention what paper you are using or the gelatin mix. I find
that the choice of paper has a big impact on my images. I use just two
papers - saunders waterford and fabriano artisco. Gelatin is about a 3%
solution. Like you I brush this on and do just one coat - works fine.
>
> 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.

Ammonium dichromate is not recommended - used it for years myself until
someone made me take a proper look. It stains much more than potassium is
harder to clear out of the print. Use a 15% solution of potassium, its a
little slower but gives cleaner results. As others have asked - how long did
you leave the coated paper? I would recommend printing as soon as dry (about
40 mins to 1 hr max). Left for about a day I find the emulsion has hardened
somewhat on the paper, leaving a stain and making it difficult if not
impossible to clear the highlights.

I might suggest too that you investigate the Linel brand of pigments.
Superior to anything else I have used. Offer much greater intensity and
colour saturation with very good control of staining. Your initial pigment
to gum ratios mentioned below could cause staining problems with most
pigments.
>
> 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.

You don't mention your light source. Gum can be rather sensitive to heat -
too much and the coating hardens. Some light sources put out a lot of heat
which for long exposures can cause problems. You should also watch dense
negatives and contrasty negs. A nice flat neg with not too much density
works best in my experience.

What kind of printing light are you using?
>
> 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

Hope that some of this can help

>
-----------------------------------------------------------------------
Hamish Stewart - Gum Bichromate Photographer - visit
<http://www.gumphoto.fsnet.co.uk>
for gum bichromate images, technical information and links to recommended
resources on alternative photographic processes.
mailto:<hamish@gumphoto.fsnet.co.uk>
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