Blue John Gemstone
Blue John is Britains rarest mineral first discoverd at Castleton by the Romans almost 2000 years ago. And are the worlds only known deposits of this extremely rare and beautiful stone.
During excavations at Pompeii two vases of Blue John Stone were supposedly unearthed, evidence therefore that the Romans not only discovered the stone but also appreciated it for its ornamental value.A "lost" deposit was rediscovered in Treak Cliff Cavern in 2013,and in 2015 a new vein, the first for 150 years, was discovered close to the tourist route in the same cavern.
Before they can be worked, the stones (having been air-dried for at least a year) are heated in an oven, then placed in a bowl of hot epoxy resin (previously, pine resin was used), and then further heated in a vacuum oven. This drives out air from minute pores in the stone, and replaces it with the resin, which binds the otherwise friable crystal structure, allowing it to be cut and polished. After resining, the stones are cut on a circular saw. They may be made into rough cuboids or cylinders ("rough-outs"), for turning as bowls and vases, or flat slices, for making jewellery.
Rough-outs are glued to a metal chuck and turned on a lathe, sometimes using pieces of broken grinding wheels. The chuck is removed by heating the glue, or — if the operator is inclined — a sharp tap on the chuck with a spanner. A further resining stage may take place, before the piece is returned to the lathe and polished with wet abrasive paper. A final high polish is added using putty powder (finely crushed tin dioxide) applied with a moist piece of felt.