That's depend on: 1)if you want to keep the original shape of the glasses,it may be difficult to detect the impurities in the glasses. Perhaps you can try XRPD scanning from which you can get some phase/crystal information of them. 2)if the glasses can be sliced,then ground and polished, of course it is possible to exam the impurities by SEM. In SE mode you will have morphology information,in BSE mode you will get chemical informaiton combined with EDS analysis. 3)Other possibilities, I don't know, sorry!