Compulsory guild membership during the Middle Ages forced almost all craftsmen to join Christian guilds, and prevented Jews from developing craft skills.
Only in those trades where religious laws governed the practices applied was an exception made, as in the case of bakers and tailors.
Even so, there were a few Jewish craftsmen within the Judengasse during the 15th and 16th centuries whose trades were not connected with the requirements of religious law.
They were for the most part dyers and glaziers.
The Schlüssel, for instance, was built "at the rear by the city moat" during the creation of the Judengasse for the cantor and blackdyer Itshak to live in: this meant that the dyer's effluents could be dumped in the moat bed.
Later dyers lived in the Schlüssel, including Jaakow, Dawid (who died in 1553), and yet another dyer named Jaakow (who died in 1570.
There are no records of any dyers in Frankfurt later.
Itshak's son was the glazier Leiser.
In 1515 he built the "Glazier's House", later renamed the Goldener Hase.
In 1566 there is a reference to a further glazier, Josef Gumprecht, but there are no further records of glaziers in Frankfurt.
Another exception to the rule was the armourer Zalman, a maker of weapons, who built the Korb at the beginning of the 16th.