Here are two sets of set squares made of vulcanite or ebonite, a vulcanized rubber invented by Charles Goodyear in mid nineteenth century. The ones shown on the right of the above picture were made by Elliott Brothers, London, and those on the left were made by Robson at 5 Dean Street, Newcastle on Tyne. According to Drawing Instruments, 1580-1980, this type of set squares can be dated to the late nineteenth century.
