From the History Information Station: "Object: Two obsidian blades collected among the Pomo of Lake County, and acquired by the Oakland Public Museum in 1914; green chert blade collected among the lower Klamath River peoples, which was acquired by the Oakland Public Museum in 1911; one obsidian blade found in Palo Alto. History: Obsidian is a volcanic glass that produces a sharp edge and a fine point, and is the material most frequently used for blades. Among most California peoples, the flaking of obsidian is a specialized profession. Although brittle, [obsidian] can be flaked into almost any form by a skilled craftsman. The only tool used is a flaker made of a sharpened bone. The point of the [flaker] tool is pressed against the edge of a piece of obsidian with sufficient force to break off a flake. The step is repeated until the desired shape is achieved.