I'll have to do another set of prints to do the dmax readings as one of the print got shipped off. I can do this though, just give us some time. The paper was Stonehenge.
As for archival, our chemist (Phd), says that because silica is in a pure form and is completely environmentally stable, it should have zero net effect on archival stability. Our joking test is to take a print after it dries, tape it to the front door and let it face the New Mexico sun at 7,000' for a few days. The same sun that bleaches the plastics on my car in less that 2 weeks. In that highly unscientific test, it behaved just like any other PD/PT print.