My wife is involved with pottery. Last week, someone came into the pottery school where she works looking for clay wine goblets that are unglazed on the inside. He claimed that the unglazed pottery removes (or in some way alters) the tannin in wine. I've never heard of this, but one of the other pottery teachers who has been at it for many years seemed quite well aware of what he was talking about. However, she is not especially knowledgable about wine, so I didn't get much of an explanation.
Has anyone else ever heard about this? If so, can you explain?