Top sushi knives are usually, if not always, sharpened on a water stone machine. This is a natural stone, similar to Wa****a, that has been cut in the shape of a large flat donut. This stone spins at a relatively slow speed (a few hundred rpm) and has a thin pipe that trickles a small stream of water onto the stone's flat surface while it spins.
You can find water stone machines at high-end woodworking stores/websites; they are the sharpener of choice for woodplane blades.
(Hmmm, the bad words editor changed the spelling of the stone, which is spelled "double-you, ay, ess, aitch, eye, tee, ay")
[ 07-16-2002, 12:22 PM: Message edited by: CrisisMode ]