Borosilicate glass Medallion.
I made this medallion for an article in my Popular Science column, using a charcoal grill to melt old borosilicate test tubes down and press them into a graphite mold. Source:Theodore Gray Contributor:Theodore Gray Acquired:26 October, 2008 Text Updated:16 April, 2009 Price: $1 Size: 2.5" Composition:SiO2+Na2[B4O5(OH)4]