Blackboard ‘chalk’ are produced especially for use with blackboards in white and also in various colours. White chalk sticks are made mainly from calcium carbonate derived from mineral chalk rock or limestone, while colored or pastel chalks are made from calcium sulfate in its dihydrate form, CaSO·2HO, derived from gypsum. Chalk sticks containing calcium carbonate typically contain 40–60% of CaCO (calcite). As compared to whiteboards, blackboards still have a variety of advantages: On the other hand, chalk produces dust, the amount depending on the quality of chalk used. Some people find this uncomfortable or may be allergic to it, and according
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.