"Bizen ware" beer mugs

Bizen ware(Bizen-yaki) is one of the most famous Japanese potteries and it is characterized by ironlike hardness, reddish brown color and absence of glaze.

These are Bizen beer mugs.
My cousin who lives near Bizen(Okayama prefecture) gave me them before my leaving Japan.

It has been said that Bizen ware makes sake(alcohol) delicious and you become less likely to get a hangover if you drink sake with Bizen ware.
Therefore many famous Japanese restaurants have been using them regularly.