Metal and glass
So in other words, the smaller the metal inclusion is the less risk of cracked glass. Makes sense since copper leaf is popular in fused glass.
Also, since metals are far more maleable than glass, the metals can take a little push and pull from the glass. Still, there must be some reason (physics, chemistry) why one can mix 90 COE glass with 248 COE metal with fairly stable results but combining 90 COE glass with 96 COE glass is usually a disaster.
Thank you for your answer, Stephen. It is greatly appreciated.