Rackwork polarising magic lantern slide with hand crank and brass rod control with rotating coloured glass polarising discs which change the image from purples to greens and vice versa.

In a rackwork slide one glass disc revolves in front of another. The moveable glass is mounted in a brass collar with a series of vertical teeth around its upper edge, forming a rackwork rim. A steel pinion with a matching toothed-end engages the rackwork and a handle is fixed to its other extremity. On turning the handle the rackwork is driven round by the pinion causing the glass to rotate.