What is yakkan?

Some articles on yakkan:

Tetsubin - History
... are the tedorikama, the toyama, the mizusosogi, the dobin, and the yakkan ... The yakkan is the closest relative to the tetsubin, the main difference is that the yakkan is made from copper, whereas tetsubins are traditionally made out of iron ... when a perfectly usable vessel such as the yakkan would have worked ...