Here are some favorite resource materials I have relied on for information in learning about glazes

The Complete Guide to High-Fire Glazes: Glazing and Firing at Cone Ten
By John Britt
Published by Lark, 2004

Out of the Earth and Into the Fire: A Course in Ceramic Materials for the Studio Potter – Second Edition
By Mimi Obstler
Published by The American Ceramic Society 1996, 2000

The Potter’s Dictionary of Materials and Techniques – Fifth Edition
By Frank and Janet Hamer
Published by University of Pennsylvania Press first in 1975, current edition 2004

INSIGHT computer software
Digitalfire Ceramic Software
Developed by Tony Hansen in Alberta, Canada

I have learned a great deal from following queries and responses on ClayArt – an online listserv that is owned by Mel Jacobson.

If you have questions about whether a glaze is food-safe, you can send a sample for testing to Brandywine Science Center in Pennsylvania.  For details, check out John Britt’s excellent page that describes the process.