So I bought a couple thousand astral shards and started gold rolling.
After about 500 shards spent, it finally popped up on a roll of 97:
So, let's take a 'nice' looking armor - Cormyrian Scalemail!
Use the mirror and put it in:
The result - a cosmetic armor (you also keep the original armor!):
Slapping my normal armor on - yep, keeping the look of the cormyrian scalemail:
It doesn't even bind!
Also works on helmets (time to farm VoN6, lol).
TL;DR: With the Mirror of Glammering you can convert the look of any armor into a cosmetic armor.
Awesomesauce turbine!
(Except for the part that it is only available on gold rolls )