There actually were dry collodion glass plates for a time -- they were replaced by gelatin emulsion because it was both much faster (even in the 1880s) and much safer to make. You're unlikely to find a dry collodion plate made after 1900, if even that late.
Donald, thanks for that point...
I've used dry collodion paper (Collodio POP), but newer have seen dry collodion glass plates myself. My oldest dry plates were made in the 1920s.