Here is an excellent article on all techniques of enamel photography and its pdf version for safe. I created from html file and few small pictures are lacked but all recipe charts are there.
''A number of readers have requested information concerning the procedure. There are several workable methods, each having some advantages as well as disadvantages. None are extremely complicated, but they all require careful attention to details and the ability to accurately duplicate each step time after time. We hope, as a result of this series, a few enamelers will spend the time and effort required to develop the skill to make and promote enamel portraits for home and museum viewing. The accomplishment is very satisfying.
The history of enamel photography is so interwoven with the history of photography in general that we feel the best way to cover our subject is to give a brief chronological history of photography, indicating when enamel was involved. We will then describe, step by step, several methods which most readers will be able to master. In addition general directions will be given for other methods.''