Today I was looking up what the author had to say about mirrors;
Position of the Mirror.The importance of good light aside... remove the collar?
The mirror should hang between two windows if possible, so that when you look into it the light will fall directly upon both sides of your face. You will then be able to get a good reflection of either side. Remove the collar. To prevent soiling the shirt, place a towel around the neck in an easy, comfortable manner, pinning it at the side.
Turns out that a well dressed gentleman a century ago not just shaved in his shirt, but said shirt had a detachable collar like this one:
While we might still slit our throats with out razors, at least our shirts aren't going to be the end of us these days...