Plexiglas, Bakelite, sheet metal, steel, die-cast zinc and cardboard. Amid the technology fad of the 1920s and 1930s, rapid advances in industrialization quickly found imitators in the toy industry. One of the finest examples is the "glass motor" introduced in 1939 by Nuremberg toymakers Gebrüder Schmid. Here one gets a look into the technical secrets of an internal combustion engine. Detailed assembly instructions explain how to build a transparent model out of forty parts, including a four-speed transmission, a clutch, the engine block, a battery-powered ignition, and a water cooling system. The assembly could be moved with a hand crank. But its very special feature was the use of Plexiglas. This new material, which had just been invented, brought the engine's functions – normally hidden away – into full view.