Devitrification is the process when glass (a super cooled liquid phase) decides to form crystals (opaque/white) of it's oxide components.
I haven't seen or heard of this phenomenum in connection with optical lenses ever. Blooming yes, but not Devit (not my invention but the usual expression amongst glass blowers).
In connection with my rebalsaming, I had a Swift landscape meniscus under treatment from the 1890's where a single surface (new glass from Jena, perhaps) suddenly became opaque. This happened at about 100 degrees C. The appearance is crazed and slightly whitish.
Fortunately, I have a replacement achromat!
If this can happen at 100 deg. then it can probably happen at longer temperatures too. Any more cases out there?
Perhaps some of the famous cases of abandoned glass types from Jena were due to this, rather than the "too soft" and "weathered badly" excuses I have been printed?
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