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
Devil sticks Devil sticks The manipulation of the devil stick (also devil-sticks, devilsticks, flower sticks, gravity sticks, or juggling sticks) is a form of gyroscopic juggling or equilibristics, consisting of manipulating one stick ("baton", 'center stick') between one or two other sticks held one in each hand. The baton is lifted, struck, or stroked by the two control sticks ('handsticks', 'sidesticks', or 'handles'), stabilizing the baton through gyroscopic motion. Devil sticks are believed to have originated in China in the distant past, in the form of simple wooden juggling sticks. Manipulating devil sticks is one of the circus arts and is sometimes