Re: Cyanotype toning and lead acetate.

Hi Christina,

> My understanding is that tannic and gallic acids make a stable and permanent compound, ferric gallate or ferric tannate--I got this from Ware's Cyanotype book (a must have if you are going to do a lot of cyanotype). <
Mikes book is really a must have!
Ferric gallate and ferric tannate are very stable. Ferric gallate ink is used since about 2000 years, medieval books were written with it and it is still expressly required for signing international treatys. Sometimes I say to other alt-printers working with platinum or cyanotype that "your photos will hang in museums in 500 years because nothing else from this period has survived". This may sound emphatic but to my best knowledge it is very near to the truth (gum, carbon and pigment prints may survive too). If a cyanotype or toned cyanotype changes its colors the acidity has changed or a compound was not completly washed out and humidity is involved. Then a chemical reaction causes the color shift. But thats nothing the process is guilty for.

> But as far as the lavender colors you may get from alkalinity, they are not stable--just return a print to an acid state and you can watch it turn blue again. <
Id say: try to ph-buffer it. I mean nothing else than as a last step wash the print in a strong solution of the (crystaline, not vaporous!) stuff that gave the print its color with an atagonist adjusted to the desired ph. Then the excess mass of the buffering agents will buffer the influence of other involved compounds. And no, Im not maniac about ph but cyanotypes are so ph-senisitive that they could be used as sensor stripes.

Cordically
  Kai Hamann
Received on Sat Apr 22 06:50:30 2006