At least you did not have a problem a person had in the early 1960s. The
spectacles were plastic frames and glass lenses and were as you suggest left
in the sun on the dashboard. All of a sudden there was a mild bang, and
there were two arms and hinges, two lenses and a little blackened bit of hot
plastic left.
I guess the material was not thermally stable. Just as well nobody was
wearing them at the time, though to get that hot I suspect the person would
be in great distress by that time!
Somebody mentioned nitrates in the mix but I'm no chemist.
Brian

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Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
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"therustyone" wrote in message
...
Fixing an old broken pair of specs with epoxy it seemed a fantastic idea
to accelerate curing by sticking them in the oven at 45 deg. C for half an
hour.
While this certainly cured the glue, I noticed very slight crazing of the
anti-reflective coat for certain angles of light, just like you get on old
glazed pottery. Not sure if this was there before, and it hasn't visibly
affected their optical quality.
Searching on the web I found this is a little-known problem caused by
differential expansion. Bloomed specs should be kept cool, for example not
left on the dashboard in the car in the summer sun.