From the book mentioned above:
He ended his apprenticeship aged 26, i.e. in 1775 and became master in 1785.
The span of ten years is rather long and not documented, but the process of entering the guild as a master was not easy. As recorded from other guilds, the candidate was given a task to make an item and it was inspected by all masters of smaller guilds or by several masters chosen to inspect finished item. According to some guild proceedings every flaw was recorded and the master (not the candidate!) had to pay penalty to guild`s treasury.
The list of his apprentices:
Juergen Christian Siemsen 1785, Johannes Diedrich von Hein 1788, Friedrich Samuel Fenton 1791, Johan Christian Tofohr 1795, Johan Gotlieb Boldt 1802, Johan Friedrich Boldt 1804.
I suppose this is rather comprehensive biography for an 18th century silversmith.
The mark that looks like a "Ж"
is actually Hamburg coat of arms (simplified).
So, all marks we discussed are on wine label. Have you searched for any marks on stoppers and the stand? Decanters are obviously of different origin, but still, if made of silver, should bear marks.
Regards