Tiffany & Co.’s third-quarter net income fell, stung by a higher-than-expected tax rate, ongoing economic weakness, and high precious metal and diamond costs. The jewelry company’s results missed Wall Street’s expectations and it cut its full-year forecast. It posted earnings of $63.2 million, or 49 cents per share, compared with $89.7 million, or 70 cents, a year ago. Analysts forecast earnings of 63 cents per share. Sales rose 6 percent in Europe and 3 percent in the Americas region. Tiffany now expects 2012 earnings of $3.20 to $3.40 per share, down from a range of $3.55 to $3.70.