Those are the element

[Anonymous]

Those are the element abbreviations:

Se = Selenium

S = Sulfur

Cu = Copper

Pb = Lead

You may also want to try this chart directly from Bullseye – it is relatively new:

http://www.bullseyeglass.com/methods-ideas/glass-reactivity-chart.html

Paul

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Paul
FusedGlass.Org
Helios Kiln Glass Studio
PaulTarlow.com