Barcol hardness test the Barcol impressor was developed by Walter Colman as a hand-held, portable means of assessing the hardness of a material during World War II. The United States Army Air Corps required a hand-held method of checking the hardness of rivets due to concerns that aircraft could be sabotaged by replacing normal rivets with soft lead or wooden ones which would fail during flight. The impressor operates when the tip is pressed against the material in question. The hardness of the material determines how far the tip indents and this is transferred by a tension spring and lever to be read
Walter Janka exile in Mexico, where together with Paul Merker and Alexander Abusch he founded the "Free Germany" (""Freies Deutschland"") movement. In Mexico he ran the publishing business "El Libro Libre", which also employed the exiled German writer Anna Seghers. In 1946 Janka took on the leadership of the Mexican section of the German Communist party (KPD). After the end of the Second World War Janka returned, in April 1947, to what was Soviet occupation zone, later to become German Democratic Repbulic in 1949. In 1947 he married his long-standing partner, a translator called Charlotte (Lotte) Scholz. The couples' two children, André