Heliozincographed is a dead giveaway for Survey of India maps.
            Currently, eleven sheets are known, with variants. These sheets were
            printed on silk. These maps do not have an edge treatment to retard
            fraying. These sheets are usually a light gray or dark grey. If there is
            any color, only blue and sometimes red was used.
 

            These sheets are printed on Silk. There are twenty-seven different RAAF silk
            maps known. They are always printed single sided. These maps do not have
            an edge treatment to retard fraying.
            Black is the predominate color of these maps.