An informative and useful article is now available online.  Here is the link:

http://www.generalintention.com/research/2012/7/7/the-shamans-mirror-ancient-animism-tool-of-shamanism.html

It was written as part of a thesis by the author, Walter Cooke, whose site is dedicated to healing practices.

The article explores the history and context of of these mirrors, as well as their use and the variety of qualities they may possess.

Copyright remains with the author, who has kindly given permission for this link.