Pre-contact Eskimos and Aleuts figured out how to boil water without the use of metal pots. Birch bark baskets and grass baskets were used. It takes patience and diligence to make sure you do not burn the baskets. By using a slow heat over coals, without any flames, and keeping the baskets full of water is the trick. The Native peoples of Alaska learned how to weave grass baskets so tight they held water. This is quite the art and very difficult to do.