It's easy enough to imagine ways in which convex grinds are achieved on new blades, but concave? ... I imagine it basically has to be done by holding the blade against the convex surface of a grinding wheel. Does anyone know? ... In which case, how are are concave blades polished? You wouldn't be able to use flat stones to contact the hollowed out parts, or do the makers actually use high-grit wheels?
Also, how prevalent are concave and convex grinds? I imagine it depends on which knife - so let's say with Japanese-made gyutos, for example. Which is more prevalent?
(Apologies if this has been discussed before, but I did try to search around...)