Re: Types of Gum? Dyes instead of pigments?
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 bichromate 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. Gord -- 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
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