Hello All I just subscribe the sundial list. I've known that this subject was discussed not a long time ago and the conclusions were not conclusive. I read in an old book, about the ability of the varnish obtained from a turpentine solution of Judea's asphalt, to be photosensitive to UV radiation, and the parts exposed become insoluble to the same turpentine. I've made some experiments under sunlight and UV lamps and some of those under sunlight gave encouraging results. The major difficulty is to measure the amount of sunlight because of it's intermittence, and the protection from rain or moisture condensed between the metal plate, photolitho and the glass plate that holds it. Is there anybody who could help me? Sergio Doret
