I have three altoids tins inuse, one of which I shined up pretty nice but not quite "mirrorlike". Now, I'm thinking here without knowing for sure: if you glue mylar or any other clear substance on the lid, won;t that reduce the reflectivity (is that a word?) of the lid? I'm thinking that you wouldn't want to glue it down, just fasten it there temporarily. Then, when you're ready to use it, you would take off the protective coating. My theory (untested/unproven) is that, any clear substance adding depth and covering the mirror will reduce its effectiveness.

My solution has been to cover the polished surface with clear tape that I remove when using the "mirror". This slows oxidation (at least the tape I've been using) and keeps the surface ready to us (this emulates what I've seen commercially). Seems to work for me in Delaware's humid and corrosion-prone atmosphere.

Reflectivity is the right word, so is albedo.

If you want to make a mirror out of an altoids tin, I'm not sure it is possible. The material is very prone to bending and denting, and it probably isn't very reflective because of the alloy involved.

I agree with Stretch, Micro Mesh might work, that's what we use at work on metal and glass. We've made an awesome mirror out of LT-80 Tape (Aluminum Tape) at work. We used aluminum oxide for the final polishing.


Micromesh

I don't know about your Altoids polishing endeavors, but I always thought this "alternate mirror" thread was a neat idea: http://www.equipped.org/ubbthreads/showflat.php?Cat=&Board=survival&Number=65328

Dremmel, felt wheel, polishing compound.