Silver closed up 6.5 percent on Friday at $31.49 an ounce, its highest level since 2012. It has surged 32 percent so far this year, outpacing gold's gains and becoming one of the best performing major commodities this year. The rise in silver prices has been driven by a variety of factors, with high investor interest and an increasingly optimistic macroeconomic backdrop. The market is expected to see a shortage for four consecutive years. Silver's rally accelerated on Friday, driven by spillover...