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
Sidewalk chalk to use anamorphic drawing when drawing with sidewalk chalk. Nonanamorphic drawing are drawings that are drawn to be observed face-on, whereas anamorphic drawings are drawn to be observed from a different viewpoint. Julian Beever, in a Q&A with Adam Boretz, explained his drawing of his first anamorphic sidewalk chalk drawing, Swimming Pool: Sidewalk Sam was well known in the Boston area for his reproductions of European masterpieces, chalked or painted on the sidewalk. Sidewalk chalk Sidewalk chalk is typically large colored (and sometimes white or cream) sticks of chalk (calcium sulfate rather than rock chalk, calcium carbonate) mostly used for