Daqq made a plasma ball made out of an old nixie tube – Link.
Basically, a plasma ball or lamp or however we decide to call it is a glass sphere/other shape filled with very low presure gas (ussually neon) and a tesla coil (or any similar resonator based power supply) or other high voltage power supply with AC high frequency output. In theory it is very easy to make one, if you have access to low presure neon pumping facilities, custom made glass and a tesla coil. ;-) The scientifically more correct explanation of how the plasma ball works can be found here. The father of the whole plasma ball is Nikola Tesla. So treat it with respect.
Now. To avoid buying thousands worth of gas pumping equipment and a glass manufacturer I decided to look for alternative sources of low presure gas filled glass items. And guess what! A nixie tube! The basic principle of the nixie tube is an inert gas discharge, where the gas becomes conductive at low presures and high voltages and even glows! That’s why nixies work and have that beautiful warm glow surrounding them.
A close look at the contruction of a nixie shows that it’s full of metal, which is conductive and connected outside.