The variety of firing methods suggested by my readers are as varied as the methods I've found since I "hit" the books again. Lynette fires at 1112F for 30 minutes, then 968F for 2o minutes with no problem. Zoe fires at 1300F for one hour, with no problems.
The very first book I used to teach myself metal clay was CeCe Wire's "Creative Metal Clay Jewelry." Looking back at that book I see that she recommended firing at 1470F for 25-30 minutes, crash cooling to 1000F and leaving it alone until the kiln is room temperature. (But I also see in my handwriting..... PMC3 1110F for 30 min.) Did I fire at that temperature or did I fire at 1470F? (Another important reason to keep good notes...... especially at my age. I celebrated another birthday a few weeks ago!)
This past summer I took a class with Barbara Becker Simon. In my notes from that class, I see that she said glass fuses to metal clay at 1470F if fired for 45 minutes. In her book, she does mention this again, but does make the comment that "the glass may flow slightly and fuse to the metal." (Yeah, this is one time I noticed that happening although it didn't the other times I worked with the glass.) Firing for 45 minutes at 1110-1200F will not fuse the glass to the metal and will need some type of mechanical hold. (That is in my notes too.)
Sherri Haub recommends ramping the kiln at 1500F per hour and firing at 1290F for 10 minutes. At the lower temperature there shouldn't be a need to crash-cool.
Mary Ann Devos also says to ramp up slowly and fire at 1110F for about 45 minutes.
Another thought was that the piece of glass was defective and I'm inclined to think that too. The crack was parallel to the backing which makes me think that maybe that layer was not totally fused. Oh well, I'll still try firing at a lower temperature and see how it goes. Thanks to everyone who commented. I do appreciate your input.