A platinum and diamond pocket watch owned by legendary criminal mastermind Al Capone has impressed collectors at auction in New York.

The Antwerp World Diamond Centre (AWDC) has completed a marketing campaign that features a gumball machine filled with lab-created diamonds that can be won for €5 ($AUD8.90).

An Australian jewellery retailer once popular with so-called Hollywood stars and local trend-setters is in hot water after a flood of consumer complaints.

A class action has been filed against jewellery chain Helzberg Diamonds, alleging that the company’s website inaccurately claims products are being offered at discounted prices for a limited time.