I would try a Dremel tool with a diamond wheel. Don't know if the wheel is available, but that would be my first approach.

It's likely to be an outside job and requiring a dust mask and goggles.

For cutting pottery and stoneware (not glass, tho'), I think a Dremel with a cut-off wheel will do the job- but it's going to be hard to made a neat cut and might take more than one wheel (don't use those paper thin wheels that come with most Dremel kits). And, yeah, it's gonna be a dusty job.

I've bought after-market mandrels that fit Dremels that take a large diameter cut-off wheel (2" dia., 1/4" center hole)- the type that might be used in an air-powered die grinder but it beats the hell out of the tool. I thought the first mandrel I bought WAS a Dremel but I note that they don't sell one that size anymore- perhaps because the tool couldn't handle it. Buy a flea market cheap-o knock-off, use-once-and-throw-it-away if that's the case.