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
Liquid chalk However, some gyms require liquid chalk because it leaves less residue on gym equipment. Liquid chalk adheres to the hand better, reducing the need to re-chalk. Some liquid-chalk mixtures for climbing are made with magnesium carbonate, colophony, and ethanol or an alcohol that dissolves the colophony and quickly evaporates from the solution (as isopropyl alcohol or ethanol). Sometimes, resin or rosin is added to increase gripping properties or an additive for aroma is included because of the bad smell of spirit. Sports liquid chalk is sold in bottles. The user takes a small amount into their palms, spreading the chalk