This begs the question, where is the hard data on the sensitivity of these processes?
The UV absorbance of dichromate is reasonably well documented. IIRC it is just a single strong absorbance peak around 370nm. Since there are so many different variations for Pt/Pd, I'm not sure if their sensitivities are all the same. Same for the difference between traditional and Ware cyanotype.
If someone had access to a UV-VIS spectrophotometer, it would be trivial to measure the various coating solutions...
Looks like Solar Tech has added a new product to their lineup, the SunUVStation.
If a product like this could give you a reliable measure of the UV present at any given time, imagine the convenience of being able to make sun exposures with as much confidence as indoor exposures with UV-units.
The issue is whether the UV-Index is useful for determining alt-exposures. Here is a good description of the UV-index and how it is figured. You'll see that they are well below the useful UV peak of 370nm for printing, but, are these values consistently proportional to slightly longer wavelengths and thus able to predict alt-exposures?