Trever Talbert uses Morta (bog oak, a partially petrified oak). Bog wood is wood extracted from trunks of trees that have been buried in peat bogs and preserved from decay by the acidity and anaerobic bog conditions and the tannins leached out of other plant matter. It represents the first early stages in the fossilization of wood, with further stages ultimately forming lignite and coal over a period of many millions of years. For many great examples of this interesting pipe wood see Trever's Morta Pipe Gallery. Also, Trevor's describes the process of finding, harvesting, and making pipes from Morta here.