i use regular window glass - you want to get the thin-est glass possible.
oh, in the book they sugget mixing developer stock solution with the developer to increase the speed. after speaking with bob at rockland colloid, it was suggested that one doesn't do that ...
if you haven't been to alternativephotography.com there is a section on dry plating that is really helpful. the person who wrote it ( scott ) is really nice and responds to emails too