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.
Don't put your specs in the overn
Sep 30, 2017
1 Replies
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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