I am also working with inorganic media, mostly semi-hydroponic, though I have a few in a 50/50 mix in traditional culture. I find that the top layer dries out to fast if I don't put some sort of "lid" on it--at the moment, small aquarium gravel. The beauty of growing this way is no more throwing away rotten bark (Terry Root used to repot 2 x a year at the Orchid Zone). What a waste of time and resources. Many of the Paphs and Phrags in nature are already growing at least partially lithophytically. Air to the roots is, I believe, an essential ingredient in any orchid culture, and probably the ratio varies by genus and perhaps in some cases even species. Thanks, Ray, for taking the lead on this and for doing your work scientifically and reporting it.