[censored], or a glass mirror that broke on them?

Ive got a few of the plastic mirrors, and the bags they come in or the plastic protective films they come with seem like mere figleafs - not much protection at all. Same with the glass mirrors - no much protection in the packaging at all.

I like glass for some applications (flight vest) and a Rescue Flash™ (LEXAN® polycarbonate) Signal Mirror in my backpack. They are stored such that they aren't given the opportunity to get scratched or broken. I wouldn't carry a metal mirror.

First, welcome in.
Second, you see the language sensors already caught something.

I have both types of mirrors, and use the commercially available protective sheets that are designed to protect smart phone screens (specifically iPhone) on all my mirrors.

I have yet to have one scratch, but I have broken a glass mirror in a fit of clumsiness.

I just went to look that the signal mirror in my EDC, its a Coghlans #9900 signal mirror. Cracked. Along the back with three veins. Mirror itself is fine. Probably put some duct tape or clear vinyl tape over the back till I replace it.

I'll weigh it out and look for a lighter replacement.

Have one in my hiking/ biking kit for 5 years in - will go take a look at it.

Is there any real difference for survival purposes in first-surface (reflective coating on the front) and second-surface mirrors (reflective coating behind the glass)?

I am surprised that Corning, with all its experience in glass and ceramics hasn't come out with something useful, highly reflective, and unbreakable (or nearly so). They do so much for optics and space materials that one might think they would have something, and we just haven't heard about it.

Sue

"vacuum desposited mineralization" means an aluminium coating evaporated onto it - since that's the standard way of making a mirror for about the last 80years that's not too surprising.

You can put a coating on the front of a surface - the advantage then is that the base material doesn't have to be transparent. But it is liable to get scratched.

Or you can coat the back of a transparent material. This is how almost all mirrors are made unless you work in an optics lab. The disadvantage is that a small amount of light (6-7%) reflects off the front surface - which doesn't matter for a rescue mirror since it's going in the same direction as the main light.
The advantage is that the mirror surface is sealed and so can't scratch. If the seal is airtight the reflectivity is higher than for a front surface mirror since aluminium drops to about 60-70% reflectivity on contact with air.

The advantage of a glass mirror is that it can be made stiffer and flatter than plastics. Any surface error or overall curvature spreads the beam out and so reduces the power that hits the eyeball of the observer.


ps. Yes that is how you spell aluminium

Buy 2, one to practice with and one that you keep safely stored and unopened in the package in your emergency kit.

[pedant]More accurately, that's ONE way, "aluminum" being the more common way, at least in the US. [/pedant]

There's also a tiny loss to transmission through whatever the substrate is, but it's truly insignificant in this situation. As you mentioned, a good quality seal between the coating and the substrate more than makes up for it.

I have kept an ACR signal mirror on my boat for at least 5 years, and it looks as clear as the day it came out of the package. It is kept in a cubby hole at the helm,just siting, no case. CountyComm offers a nice one that comes with a nice case.