Hints:

1. The letters FS can be seen somewhat hidden in the frame ornaments for some initials (D, E, G, I and N).

2. There exists one "Potsdam" typeface family designed in 1934 by R. Golpon for J.D. Trennert und Sohn. However, they do not seem to have designed/released the "Potsdam Initials".

Thanks again.

Any clue out there? Perhaps another forum/site?

Thanks again.

Try the (german) forum typografie.info, some blackletter experts are attending there.

Or try to contact Peter Reichardt. He is one of the best in having knowledge of extinct (german) typefaces.

Another one could be Martin Z. Schröder from druckerey.de. He works, publishes and writes about old typefaces.

I had a look at the site of Dipl.-Ing. Gerhard Helzel, but have only found some lookalikes.

That's what I can recommend.

Thank you very much. I will post back if I get any positive answer from your recommendations.

Kind regards.

One thing, too: Peter Reichardt published something interesting at the Klingspor Museum. You could stroll through the metal typeface collection PDFs and maybe find something.

Thanks again for your replies. I haven't dared to try the first three suggestions from your first post because I can hardly read/write German. I also checked G. Helzel's and the Klingspor Museum's sites to no effect. However, from the first hint in my second post and from information digged from Luc Devroy's site and from F. Bauer's "Chronik der Schriftgießereien in Deutschland und den deutschsprachigen Nachbarländern" (set into PDF by H. Reichardt in 2011), I discovered that one Friedrich Schoch (FS) designed around 1840 a typeface ("Schochisch") on which the 1900's "Neudeutschen Schriften" seem to have been based. Solo's "Potsam Initials" fit perfectly with those typefaces, so joining everything together it is my (possibly wild) guess that those initials were originally designed by the "Schriftschneiderei und -gießerei Friedrich Schoch" ca. 1840. I'm afraid I can't go further, so any evidence or oppinion supporting/rejecting this guess will be mostly appreciated.