Good to know that this would [probably] work. I'd be surprised if nobody's tried this before, as everything seems to have been tried at one time or another (and everytime I come up with a good idea, it almost certainly turns out to have been done). Once I get my tannic / gallic acid extracted (another project), perhaps I'll try this. The only iron compound I have is yellow ferric ammonium citrate - is that light sensitive enough?
Is this to say that the two-step method is faster than the print out method, perhaps even in-camera fast? Or am I reading incorrectly?was abandoned for the mixed sensitizer, printing-out processes for cyanotype, chrysotype, and kallitype before there were photographic negatives to print, and before anyone tried Herschel's original (much faster) method in camera.