Donald,

I thought my last response addressed directly your question. AZO has sensitivity well into the visible light range, and it is the radiation in the visible range that is providing exposure, not UV light. Your reflector flood lights probably emit little or no UV radiation, but the AZO material is exposed nevertheless because it also has considerable sensitivity to light in the visible range.

What I am saying is this. You can expose AZO with a UV light source, which matches the greatest spectral sensitivity of the paper, but your exposures will be really short, too short for most contact printing conditions. Or you can also use the spectral sensitivity of AZO that is in the visible range and make the same exposure with lights of much greater wavelength, *but* your exposures will be much longer.


Regarding Bob Herbst's tests, note simply that AZO is capable of a much greater reflective density range than platinum or palladium. The maximum reflective density possible with platinum or palladium is around log 1.5, whereas AZO is capable of readings approaching or in excess of log 2.0.

Finally, I do not indicate that there is a differing effect on the transmission of UV light as it applies to AZO. If people were routinely using UV light sources to expose AZO, instead of light sources in the visible range, then we might assume that the density range requirements of negative for AZO and Palladium printing would be about the same. But the fact remains, folks are exposing AZO with light sources that produce little or no UV radiation.


Sandy