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
Chalk talk use of colors and techniques and the approach talks about the easy use of chalk talk with unnecessary details which can be carried out quickly [makes no sense]. People who are not familiar with this method and would like to give this method a try, this is a perfect book to get access to. A chalk talk was a popular act in vaudeville. A performer used chalk on a blackboard to make changes in a drawing while delivering a monologue. Some performers would do caricatures of audience members. The term also was used to describe an act done with crayons.