Yes, silver is right. Not sure whether 925 or something else though. The GDR issued those medals in different versions; here are 11 copper pieces:
http://img.muenzauktion.com/polland...combined.jpgThis auction catalog lists 12 in silver, €100 altogether:
http://www.tempelhofer-muenzenhaus....235x1323.pdf(item #1289). The following ones, 1290/1291/1292, are packs of Cu-Ni medals: one lot (70 pieces) is €50, another one (140 pieces) is €90. The gold ones are more expensive of course; about €1,000 per medal.
And "Junker Jörg" was Luther's "pseudonym" while he lived and worked at the Wartburg. As for the country name; I don't know why it it would be "
DDR" in English. :) Yes, that is the short version of the country name in German. But in English the full name was "German Democratic Republic", so "GDR" would make more sense to me. Plus, you won't get into trouble with this wrong linkification. ;)
Christian