These cases were often made of cardboard covered with leather so that they could be unfolded on a desk or table like a wallet. As with other styles of cases, American retailers including Eugene Dietzgen typically imported high-quality drawing instruments from various firms, such as the German workshops established by Georg Schoenner and E. O. Richter; assembled the pieces into sets; and imprinted their own company names on the top of the case or inside the lid. In addition, Schoenner and Richter both sold their products directly to individual Americans. World War I and World War II interrupted the availability of European instruments, particularly those made in Germany, leading to increased efforts to manufacture items such as drawing compasses in the United States. The people who purchased sets of instruments also sometimes marked them with their names and addresses, suggesting that they carried their sets from home to work and did not want the sets to be misplaced.