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Is the devitrification throughout or just surface? If throughout then you probably wont be able to manage to obtain an optically smooth finish.
My blanks are float/plate glass cut from viewing panels(ex sea aquarium). No devit, very good anneal, very flat both sides (probably within 4 waves).
Blanks have been ground/polished/figured and in number of working scopes. Some figured to better than 1/20 wave, 0.99 Strehl.
Stephen.
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