David McLaughlin pawned other valuables entrusted to him by clients and fobbed them off by pretending they were in a safe or he had to polish them.
The total value of the jewellery is thought to exceed £70,000, with incalculable sentimental values for 66 owners of missing items.
McLaughlin, 45, is facing jail after admitting fraud and theft at Goldsmith in Irvine, Ayrshire, between November 2009 and December 2010.
McLaughlin, of Irvine, was "embarrassed and ashamed", Kilmarnock Sheriff Court heard.
Sentence was deferred until next month for reports and McLaughlin was bailed.