By many lines of evidence we are led to believe that obsidians in course of time suffer devitrification, in other words they pass from the vitreous into a crystalline state, but as the changes take place in a solid mass they require a very long time for their achievement, and the crystals produced are only of extremely small size. [Please select]
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Devitrification is one of the worst faults glass can possibly have. [Please select]
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A flame with a little tinge of yellow should be used for this operation to prevent devitrification (page 2), as the thick glass shrinks slowly. [Please select]
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