I’m going to concur with Brian, though without any certainty. Craftsmen and styles travelled about Europe, and were practiced at various times and places. However, the OP’s key could well be venetian/italian, renaissance (say 17C?), and, as he hinted, quite likely a chamberlain key rather than a functional one.
Although lost wax casting seems an obvious way of making such bows, all I have seen have actually been brazed. Zinc, incidentally, was used long before its identity as an element was certain.
On books, afaik, making ‘steel’ is first recorded in the 17C (from memory, Agricola); but the Romans certainly used steel knowingly, and many mediaeval tools had steel edges welded on. So indeed, books must be read with care - they are rarely complete.
