Radium electroplated on a very small sample of copper foil and covered with polyurethane to prevent reaction with the air.
<a href="//commons.wikimedia.org/wiki/User:Grenadier~commonswiki" title="User:Grenadier~commonswiki">grenadier</a>
CC BY 3.0
<span class="int-own-work" lang="en">Own work</span>