| http://www.w3.org/ns/prov#value | - They pass through a viscous stage in cooling from a state of fluidity; they develop effects of colour when the glass mixtures are fused with certain metallic oxides; they are, when cold, poor conductors both of electricity and of heat; most types are easily fractured by a blow or shock and show a conchoidal fracture; they are but slightly affected by ordinary solvents but are readily attacked by h
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