GB428952A - Improvements in and relating to blackboards - Google Patents

Abstract

428,952. Educational appliances. GAMBLE, G. M., and McQUILLEN, W. T., Royal Military College, Camberley, Surrey. Dec. 28, 1933, No. 36449. [Class 146 (ii)] A blackboard comprises in combination a plate of magnetic material having a coating of paint on the face of the plate of such matt surface as to permit of marking with chalk and of ready erasure of markings, and a number of symbols or models each of which comprises a magnet strong enough to hold the symbol &c. to the magnetic plate on its painted side. The blackboard consists of a light frame made in two parts hinged together and provided with a catch so as to be set up as an easel, and the frame is covered on one or both sides with a thin iron plate 15 which is let into the edges of the frame 11. The frame is stiffened with plywood 16 and packing pieces 17, and the surface of the plate 15 is covered with a matt shellac varnish, having lampblack or zinc white as the colouring medium. Alternatively, the blackboard may be formed from a thin wooden board upon which is secured a layer formed of filings of magnetic material mixed with shellac varnish, size, glue, &c., with the addition of a suitable colouring substance. Symbols or models printed on or represented by plates 23 may be mounted on the blackboard by attaching the plates to horseshoe magnets 22 or to bar magnets. In the latter case, when representing models of wheeled vehicles, two wheels may be attached to each polepiece, by mounting them on a spindle having a good clearance in a hole in the polepiece. When formed of magnetic material, these wheels adhere to the blackboard surface ; when not so formed, light springs may be provided to press them against the blackboard, so that when the symbols are to be adjusted on the surface the magnets may be pulled away slightly, but the wheels remain in contact therewith and facilitate the adjustment. The magnets and attached symbols may be stored in a compartmented box, the base of which is of iron and which serves as a keeper for the horseshoe magnets. The blackboard may be used as a magnetic backing for a chart which can be attached by adhesive pins, clamps, or by means of permanent magnets, or it may be used as a suitably coloured screen on to which diagrams &c. may be projected. British Specification 19908/04, [Class 146], and U.S.A. Specification 1,879,002 are referred to.