What is "zimmerit"

Zimmerit was a paste-like coating used on mid- and late-war German armored fighting vehicles during World War II. It was used to produce a hard layer covering the metal armor of the vehicle, providing enough separation that magnetically attached anti-tank mines would fail to stick to the vehicle, although Germany was the only country to use magnetic anti-tank mines in numbers. Zimmerit was often left off late-war vehicles due to the unfounded concern that it could catch on fire when hit. It was developed by the German company Chemische Werke Zimmer AG.