Hi Leslie,
Not sure you should attempt this route
. My experience with gluing glass goes back a year or two when I attempted a 25"f4.25 sandwich mirror project. I used a not too fast curing super strong epoxy glue. At first during hogging through to fine grinding, and even when part way through polishing all looked good, (Ronchi test was ok), but there was a particular point nearer the end of polishing when the Ronchi test showed that some of the glue joints at the junction glass pillars(7mm thick) to front and back plates(each 19mm thick float glass) were failing. At that point I laid aside this project. The only way to get two glass surfaces to successfully adhere long term is too fuse those surfaces together by heating to the required temperature in a glass or ceramic kiln. In the future I may take my sandwich project to a kiln and do the "fuse". I dont know what diameter mirror your thinking on working. My advice would be to use a single good quality 19mm float glass blank (for anything 14" in diameter and less). Larger will need a thicker substrate.
