Does porcelain need to be immersed in the mikvah?
What do ashkenazim hold?
How about sefardim?
Raw earthware (terra cotta, i.e. flowerpot finish) does not require an immersion. (Immersion is for things that can become ritually impure, then ritually pure again. Clay can't become repurified, therefore no immersion is required.
Porcelain is glazed earthenware. Hence some rabbis treat it as glass, which requires immersion; and others ignore the glaze and treat it as earthenware, which doesn't. And some rabbis differentiate based on how thick the glaze is. I've heard all these opinions from non-Hassidic Ashkenazi rabbis.
My impression is that Hassidim are generally strict. I don't know about Sefardim.