Shares of Blue Nile, the online diamond and jewelry retailer, are down more than 20 percent in Thursday morning trading after the company posted “disappointing” Q4 results, according to CEO and President Harvey Kanter. Blue Nile's sales tumbled nearly 5% year-on-year in the fourth quarter. This was particularly disappointing given that the fourth quarter represents the company’s important period of holiday jewelry sales. While net sales for the year were $480.1 million, up 1.4 percent from last year, they still failed to meet Wall Street predictions of $498 million for the year. Kanter explained that Blue Nile’s poor revenue growth for the year was because customers were making fewer big ticket purchases of jewelry and because of the weakness of foreign currency. He also noted that Blue Nile’s core engagement products were selling for less.