LANGENDORF, 15 Pfg grey-violet vertical pair, 60 Pfg Prussian blue Steelworks and Dove of Peace 1920 on registered letter to Emmagrube / OS, double-circle LANGENDORF 20 3 21 * (KR. GLEIWITZ) * (OS handbook No. 181.1), interesting unusual commercial mail from plebiscite day, age and use marks typical of period