Mick, this clay I got years ago near Berlin during a really Tabakskollegium. It was amazing. There were some men in historical military uniforms (so-called Lange Kerls) they served us beer and gave us assistance with this clay-pipes.
This clay was produced in the Netherlands. It is a P.J. van der Want A Zenith pijp, Gouda Holland.
I don't use it often because of the cleaning-problems.