U of S | Mailing List Archive | alt-photo-process-l | RE: Ware's Cyano On Pot ... Instead of NH4 Dichromate

RE: Ware's Cyano On Pot ... Instead of NH4 Dichromate

Hi Michael,

I guess it can be used; the problem with Potassium is that it will make
an unsoluble compound with the Ammonium Ferric Oxalate sensitizer. But
since you're using very little dichromate for preservation of New
Cyanotype, I don't think that it will harm the sensitizer and you'll
already going to filter it anyway. FWIW, I use Potassium Gold Salt with
Ammonium Ferric Oxalate in New Chrysotype, and I don't experience any
problems with much higher Potassium concentration.


-----Original Message-----
From: Michael Koch-Schulte [mailto:mkochsch@shaw.ca] 
Sent: Sunday, April 08, 2007 8:22 AM
To: alt-photo-process-l@sask.usask.ca
Subject: Ware's Cyano On Pot ... Instead of NH4 Dichromate

Maybe someone with experience could answer, or possibly a chemist. Would
it matter when formulating Ware's Cyanotype to use Potassium Dichromate
instead of Ammonium Dichromate? My understanding is that Ammonium
Dichromate is used only as a preservative. Would the K in Potassium
Dichromate crystalise out in a similar manner as the Potassium Iron
(III) Oxalate does? Or would I be left with an excess of K ions in the
mix? My question amounts to: can Potassium Dichromate be used as a
substitute when Ammonium Dichromate is not immediately available.