L-56 Blue Zircon (tr)   

This sample is fired on copper over silver foil. 

Transparent, cataloged, England manufacturer, Blythe enamel for Copper,
Silver, Gold, Iron and Steel. This enamel is “medium fusing”
and should be fired at 1450 to 1550 degrees F.
for approximately 2 to 4 minutes.
Enamel is 80 mesh and lead bearing.