This has been bugging me since, well, lunchtime, although I’d noticed it before now.
Lots of large mirrors have bevelled edges; that is, the outer inch or so slopes down from the main mirror surface towards the wall. The one by the pool table in my local pub is like this, hence my current puzzlement.
If you stand in front of the mirror, near to one of the edges, so that your reflection is also near to the edge as you look at it straight on, you also see a strip of your face in the bevelled section. Say I am standing in front of the mirror, towards the right-hand side:
/
__________________/
mirror
* me
(angle of bevelled section is exaggerated in the diagram)
I see my face directly opposite me in the mirror, but also in the bevelled edge, shifted to the right.
Now perhaps I’m being dumb here (blame Greene King IPA if so 
) but, as the bevelled edge is sloping away from me, shouldn’t the image in this section be of the room even further to my right?
_________/ mirror
|\
| \
| \
* 0 <-- object I should be seeing
me
If the bevelling was in the opposite direction (i.e. “outwards”) then I’d expect to see my face further to the right, as observed. So what’s going on? Is the silvering bent in the opposite direction to the glass surface? Or is my understanding of optics up the spout?
The silvering isn’t bent at all; the bevel is ground into the front surface of the glass; you’re looking at a flat mirror through a prism.
To test, take something reflective and bend it as described if you can. Results will be diff than the beveled glass.
The reflective material on the back of the mirror is flat. The glass is not really doing the reflecting., just allowing light to pass to the reflective material.
Ah… that makes sense.
so picturing a light ray going from me towards the mirror, it strikes the bevelled edge, then gets refracted slightly to the left, then hits the silver, then bounces back, then gets refracted back to the…uh… hang on 
Yeah… that’s about as far as I got, but don’t forget the rays exiting through the bevel didn’t necessarily enter that way.
Moral: don’t try to think about science on licensed premises.
I just did a quick rough pencil and paper sketch of the situation as described, where Colophon is looking at (him/her?)self at the right edge of the beveled mirror. If we can assume that the index of refraction of the glass is greater than that for the air in the pub, then by Snell’s Law the angle of refraction in the glass will be less than the incident angle and so a light ray will be refracted to the left. After bouncing off the back of the mirror the light ray is refracted again as it passes back out of the glass and is again bent to the left.
So, in my sketch (drawn as if I’m looking down from above) the light rays travelling perpendicular to the back of the mirror and striking the beveled right edge of the mirror are coming back out moving to the left. To me, this means that what I should see is that the bit of my face I see in the beveled part is more to the right of the bit I see in the flat part of the mirror just beside the bevel.
I just had a little play around with some raytracing software and it made the whole thing easier to visualise. Forget that it’s a mirror - the image you see in a mirror is functionally the same as the image you see through a window (ignoring for the moment that some rays pass through the bevel twice).
I made flattish block with a bevel on the right-hand side - looking through it, the rays are bent in such a way as to shift the image to the right of its actual position - see the result here.
