[thedoc (OP)]

DON MCKENZIE  asked the Naked Scientists:
   
We have a small hand mirror which we had for 10 years one day my wife used it and it had suddenly magnified itself like a shaving mirror so we bought another mirror. A few days later we picked up the old mirror and it was back to normal. Is there any explanation for this?  

I would love to know.

Regards
Don Mckenzie, Cape Town South Africa.

What do you think?

[RD]

Extreme temperature could cause the mirror to become warped in a tight-fitting frame,
[ the mirror and the frame will have different rates of thermal expansion ]
then return to normal (flat) when the temperature became normal.
 
https://en.wikipedia.org/wiki/Curved_mirror#Concave_mirrors