Go stones can be made from many different kinds of materials - with varying prices. Mass produced stones are simply white and black plastic counters or simple blown glass. Traditional Japanese stones are made from clam shells (for the white stones) and slate for the black stones. Stones can also be made from ivory or agate for the white stones, and onyx or ebony for the black stones. Each board should come with 181 black and 180 white stones. That's one stone for every intersection on a 19x19 board, but generally games last fewer than 350 moves.