Best not to embed sterling wire in PMC. The extended firing time
makes something in the alloy do something weird, to speak
scientifically, and the sterling -- say it's wire that extends
beyond the PMC piece -- will become brittle and break off.
Then if you look in the center of the wire, it looks seriously
changed and different. It's not the silver that does this, it's
something in the other 75 parts/1000.
Use fine silver, or solder on the sterling later.
Metalsmith, Certified PMC Instructor
Hard to Find Tools for Metal Clay