Quote Originally Posted by Donald Qualls
PE, not to argue, but the recent work on cyanotype rex has demonstrated in-camera negatives, cyanotype-to-cyanotype contact printing (through heavy paper), and exposure of prints with ordinary tungsten light. The very same chemicals are vastly faster (based on my reading, it looks like several stops faster) when the sensitive iron and the colorant are separated; my hypothesis (as a non-chemist) is that light energy goes to reducing ferric to ferrous without being soaked up in the secondary reaction or absorbed by its products -- which might reasonably mean both less energetic (i.e. longer wave) light can do the job, and a great deal less of it is needed.
I don't mean to butt in, but Mike Ware does explain the ferric process on his website. I seem to recall, that Fe3+ reduces only in the presence of UV light, not regular light. In lieu of any materials on the C. rex process, I would lean on previous scientific data. Actually, Hershel did try ferric ammonium citrate by itself, and developed in various things (including potassium ferricyanide and gallic acid). His conclusion was that the citrate by itself was too slow. Oxalate might be a different story. And don't get me wrong. If the cyanotype process was faster this way, I would be near the front of the line on getting at it. But I also think that both Herschel and Ware have researched the cyanotype very thouroughly. I don't mean any of this in a mean way, just disseminating info. No hard feelings?

The Unblinking Eye has a variation on the cyanotype with gallic acid if I remember rightly.