Calcium sulfate an unusual property: when mixed with water at normal (ambient) temperatures, it quickly reverts chemically to the preferred dihydrate form, while physically "setting" to form a rigid and relatively strong gypsum crystal lattice: This reaction is exothermic and is responsible for the ease with which gypsum can be cast into various shapes including sheets (for drywall), sticks (for blackboard chalk), and molds (to immobilize broken bones, or for metal casting). Mixed with polymers, it has been used as a bone repair cement. Small amounts of calcined gypsum are added to earth to create strong structures directly from cast earth, an
Pick-up sticks (Haida) Pick-up sticks (Haida) Haida pick-up sticks exist in two sorts. There were non-decorated thin playing sticks (not collected) and the other decorated, containing three sets of sticks. These were named after animals or birds only known by the owner or his family, according to Charles F. Newcombe. The decoration consists of rings and spiral markings for distinction. Most elaborated sets may contain a Haida art gallery of more than fifty drawings. Made of maple wood, they are decorated with pyro-engravings or carvings. Many pyro-engravings are inlaid with copper or abalone shell. The drawings are complex and an artistic challenge as