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 (1842-1905). Today chalk talks are still regularly used as a method of preaching scripture visually, by evangelists that have artistic ability. A book by Jeanne Bridge, "Chalk Talk for Catechists," gives us a useful introduction to a catechetical method, where we see (what?) is an increasing interest among all sectors of people. Basically, it talks about "speaking the message" by illustrating with simple chalk drawings, along with the talk, that highlight the main points of the lesson. The word which is predominant is at a lead together with the word [this phrase says nothing], so that the word and the