Porcelain has a higher temperature than silver. After all, they
make crucibles out of glazed porcelain.
True, porcelain firing temperatures are higher than the melting
point of silver. That’s not the issue-- heat shock is. The porcelain
used for crucibles is NOT the same as the porcelain you eat your
dinner off of! High temp ceramics such as crucibles are formulated
differently from normal decorative ware. So unless the plan is to add
bails to pieces of crucibles, the porcelain is very unlikely to be
able to withstand the heat shock.
Oh, and also, I’ve never seen a glazed crucible, unless you count
how it looks after it gets a lot of flux melted on it.
On the other hand, if the porcelain pieces are cheap and
replaceable, I’m all for outside-the-box thinking!