A thermochromic drawing device is disclosed which can be marked and erased by selectively changing the temperature of its drawing surface. The drawing surface of the drawing device consists of a flexible substrate printed with thermochromic inks having at least two color states. The flexible substrate...http://www.google.es/patents/US5441418?utm_source=gb-gplus-sharePatente US5441418 - Thermochromic drawing device
