Thankl to Nic and Jason, same article...
but just what I was looking for. I have never seen mention of stones grooved below the girdle before, it all makes sense now.
I would have thought that grooving the stones would have knocked alot off their value, not something I would want to do to a quality stone.

Jason, what holds the four meeting corners in place in the centre of an illusion setting?
cheers
G