Stillpoints: I don’t know because they’re very careful not to show pictures of the ceramic balls!
(The older products looked as though they were probably using alumina.)
Finite elemente appear to be using either silicon carbide or silicon nitride (but I can’t be sure)
I don’t seem to be able to find much about Franz audio.
“The platter is produced from ceramic oxide powder…”
Taking that statement from Rega, looking at it and thinking about appropriate materials, I think sintered alumina is the most likely ceramic material for the platter (alumina is aluminium oxide). (However boron nitride is also a possibility, but on cost grounds it would surprise me if this was the case.)
@ChrisSU
You spotted it!
It’s not flat, there’s a very small, shallow, polished depression in the middle that centres the ball in normal operation. The cage is normally quite loose. To prevent this being a problem it’s made for a material that has some limited self damping characteristics and is very light weighing 0.33g.
@Thomas
The brass had to be locally hardened to deal with the contact pressure from the silicon nitride ball, so using lead (or tin) would be possible but would leave it open to transmitting more transverse vibration.
Additional differences are that
1 the lower sound velocity in lead would be beneficial in increasing energy reflection.
2 the increased contact area at the lower interface would increase energy transmission.
Unfortunately I don’t have the necessary high speed laser interferometer to really analyse the system (I don’t think the accelerometers in my’phone would be sufficiently sensitive to measure the overall effect either).