  Soda-lime glass Medallion.  
I made this medallion for an article in my Popular Science column, using a charcoal grill to melt the ingredients (silica sand, washing soda and limestone) together into soda-lime glass.  Once melted I pressed the glass (darkened by ashes from the fire) into a graphite mold I had machined and heated in the fire. 
Source: Theodore Gray 
Contributor: Theodore Gray 
Acquired: 26 October, 2008 
Text Updated: 26 October, 2008 
Price: $1 
Size: 2.5" 
Composition: SiO2+Na2CO3+CaCO3
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