After pulling out a second dried piece (Again, one that was created a year ago) I did NOT heat it in the toaster oven first. 40 seconds into the eight minutes the greenware exploded.
This could be a fluke – OR it could be because I didn’t heat/extra dry it. So I am restarting my second try – DO OVER
Subject: Flattish type button
Heated for 1/2 hour in toaster oven at 350
Microwave: 8 min, 6 min – no glow, 5 min – no glow, 4 min – slight glow, 1 min – stopped and opened.
Result: The top came away from the bottom this time, cleanly and easily. The button is white and cooked. It looks good. The button is NOT brittle. This was a good time allowance. SUCCESS
Third Try: (In the meantime)
Subject: A thicker heart, three dimensional, not flat, exactly like the one that exploded without first preheating/predrying
Heated for 1/2 hr at 350
Microwave: 8 min, 46 sec – stopped
Result: SUCCESS – For my microwave 7-8 min is the right amount of time, and preheating does make a difference.