The 3-shaped z-letter IS fairly common in blackletter. Some typefaces
actually use both forms; a crossed cap Z and the 3-shaped lowercase z.
I would assume this would have originated during the period where
fraktur hands evolved from the Carolingian but might have more to do
with the type of pen used?

The bibliographic references in Blackletter: Type and National
Identity by Peter Bain and Paul Shaw might yield further information.

Frederic Goudy's Goudy Thirty has an alt cap Z that manages to capture
the flavor of both the crossed Z and the tail-like 3-shaped letterform.

Gerald Lange
The Bieler Press

>
> So it's rather unlikely that this 3-shaped z-letter originates in

Blackletter? But

> where else would it originate?