Thank you Fred, I'm glad you like it. About the negative contrast. X-ray film I used did not produce much of a contrast in my Ansco 130 developer - I think it's inherently low contrast film. The cleared highlights resulted from my multi-layer coating approach. Now, from the letter it sounds like I did it on purpose. That could not be any further from the truth. This is my first set of cyanotypes, so the multi-coating was an honest mistake, I like the results, and maybe next time I'll do it on purpose .
The deal is, my 9 year old daughter did a first set of cyanotypes for her school project. I did not touch them, only supervised. She used Sullivan's formula, except she substituted potassium dichromate for ammonium dichromate. It produced beautiful deep blue prints. However, the coating had a few blue spots in it after drying. My initial theory was that the amount of dichromate was too much, so when I started this project, I reduced it by a third. I tried a first test print and amazingly the print was yellowish-brown like what you see in the highlights. The only issue was that it had rather low d-max. I tried adding couple more coatings from the same mix, which resulted some improvement in contrast, but still not enough. Out of desperation, I mixed the exact Sullivan formula and put another coat on the paper. And this is the result that you see. It is only one exposure, however very long. The yellow coating is slower than blue, so it causes some clipping in the highlights. I agree with you that doing some kind of registration and double exposure first with yellow coating and then with blue should produce much nicer dual-tone image. I'm only afraid it's quite a bit more than my current level of expertise.