Here is a great book that focuses on Cone 6. I keep this nearby in my studio when I am mixing the chemistry for glazes. It discusses not only the basics but how to create accurate glaze tests, fitting the glaze to your clay body, and approaches to develop your own stable glazes.
The book is full of beautiful photographs and is organized thoughtfully. Glaze recipes are included with corresponding images on various clay bodies as well.
Find more info at mastering glazes