U of S | Mailing List Archive | alt-photo-process-l | Re: Types of Gum? Dyes instead of pigments?

Re: Types of Gum? Dyes instead of pigments?

Darnit, Gord.  I had completely sworn off spending any more time with those "exotic" gums.  But I'll try that acid wash.


On 10/17/07, Gordon J. Holtslander <gordon.holtslander@usask.ca> wrote:
On October 16, 2007 1:27:22 pm Keith Gerling wrote:
> I've had considerable success using fish glue as my colloid, although I've
> found the results to be rather unpredictable.   Tragacanth I've found to be
> totally useless: it won't dissolve completely (it's odd: almost as if it
> were two gums put together - one that dissolves and the other that just
> floats around in flakes.  I keep meaning to see if I can't somehow separate
> them...)  Guar (or is it tara? - it's been awhile) will harden fine with
> dichromates, but the unhardened gum won't wash away!  It just sits there on
> the surface of the print, all "gummy".  One can remove it carefully, but
> why bother.  In any event, I've tried several gums looking for a holy
> grail, and keep coming back to plain ole gum arabic.

Keith, have you tried Xanthan Gum?  Its a little different - its a
fermentation product of sugars by a specific bacteria, rather than a plant
derivative like most gums.   I don't know if it can be hardened with a

The interesting thing about it is its pseudoplasticity.  it can form a very
viscous solution, but when shaken it looses its viscosity.  This means it
should be possible to create a well dissolved mixture of gum, pigments and
chromate, but still be able to form a reasonably thick emulsion when coated.

see http://en.wikipedia.org/wiki/Xanthan_gum

xanthan gum when mixed with locust bean gum is purported to have a synergistic
increase in viscosity as well.  Perhaps it would have this reaction with
other gums.

Guar gum is supposed to loose its viscosity in strong acids.  Perhaps a rince
in an acid solution would clear the unhardened guar gum - if the paper could
tolerate it.

Gordon J. Holtslander           Dept. of Biology
gordon.holtslander@usask.ca     University of Saskatchewan
Tel 306 966-4433                112 Science Place
Fax 306 966-4461                Saskatoon SK., CANADA
homepage.usask.ca/~gjh289       S7N 5E2