When you talk to well known pipemakers there are "secrets" you can pry out of them, and some you could pull their toenails and never find out. Sandblasting generally belongs to the second category :mrgreen: You might get some generic answer about glass bead versus aluminum oxide, but you wont get very far. JT Cookes career revolves around that beautiful blast, and I'm betting the exact technique he uses will die with him.
But the short answer I think is a lot of time, a lot of work, and a series of different blasting media and nozzles.
The results are spectacular though.