Osmium crystals tend to cling to the glass ampoule walls making dissolving them difficult. Smashing the vials results in glass shards that may get into sample vials and can be dangerous, or carry into embedding media and damage diamond knives.

A simple trick to eliminate smashing osmium vials is to dip the sealed ampoule into liquid nitrogen. This releases the osmium crystals from the glass walls. Then simply break the vial using an ampoule cracker (available through EM supply houses) and pour the osmium crystals into a bottle containing the water for the OsO4 solution. Wait a few minutes to let the ampoule warm-up, and it is easy to see if all of the crystals have been dumped out of the ampoule. Let the solution sit overnight at room temperature in a hood and the next day the crystals will be totally dissolved.