I'm pushing my luck here, and this is definitely the last (for the moment), but I wonder if the Research Brigade can come up trumps with this one?
It is a standard Prussian IOD89, plain blade but with the name C. Ambrosius engraved on the rear folding clamshell, plus a very nice family crest on the tang button. The scabbard is post-1910, black with a single ring.
Any thoughts?