To many barium will sound vaguely familiar but, like calcium, few will know that it's actually every bit a metal as iron or gold. This metal has a particularly voracious appetite for oxygen. So much so that its only commercial usefulness in pure form is to mop up errant oxygen atoms where they're unwelcome. This used to be a big job in the making of vacuum tubes but since the transistor came along barium was pretty much put out of a job. Well, except fort those barium enemas...

Due to the extreme ease with which it forms oxides, barium is quite possibly THE most difficult element to maintain in a shiny, polished state like normal metals can. So the choices are bare pieces of metal in oil with some oxidation or bare pieces of lustrous metal locked away in glass.

Note additional options for this element on the Ampules section

CAS 7440-39-3