Stephen, Try contacting the Bluethner factory: Julius Bluetner Pianofortefabrik GmbH Franz Flemming-Str. 39 O-7010 Leipzig Or, if the german language is not a problem, buy this book: "Pianofortebau" by Ingbert Bluetner-Haessler, Published by : Verlag Erwin Bochinsky , Frankfurt am Main, Germany ISBN 3-923639-92-9. It discusses a.o. the 'Bluetner Patent Action' and its regulation. Frans Sedee
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