Explanation of the Meaning and Use of a Mandala by Alexander Berzin - Munich, Germany, December 2003
There's also a recorded transcript if you wish to listen instead of reading on the computer.
Another beautiful site can be found on "Tale of Gondo Monestary" by T. S. Caladan. I found this post very interesting because it not only talks about the materials used, with illustrations of the monks creating a mandala, but also writes about the ritual destruction of a mandala ... here I discovered that once the mandala is destroyed the sand is gathered into a silk bag and returned to the earth by pouring it into a river or any other moving body of water - you'll find this information in a sort of P.S. in the second part of the post.
The first part of the post is by the author's admission 90% fiction ... but it's a really great story which I enjoyed very much!
