Kanten (寒天) is the Japanese word for agar-agar, an odd type of white seaweed
like gelatin when boiled and allowed to cool. The characters
literally mean "cold weather", and kanten is extensively
used for making Japanese sweets, especially yokan.
While I would be very hard pressed to explain how, kanten's
taste and characteristics are subtly different from and, IMHO, better
than gelatin. And in this age of BSE perhaps it's just nicer
to eat seaweed instead of ground bones.
Kanten is available as kakukanten (角寒天), in square blocks,
itokanten (糸寒天), long threads more akin to the original weed,
and powdered for instant use (not recommended). To use any
non-instant form, kanten has to soaked overnight, causing
it to swell and take on an unnerving resemblance to some of Giger's
creations. Discard the soaking water and shred the kanten
with your hands into a saucepan. Add water and boil, stirring carefully
until all the fragments have melted and the water is transparent. After this, you can add anything you want
(flavoring, sugar, etc). The liquid will congeal as it cools down.