Are gold and silver a runaway train? Perhaps. But moody investors, speculative skulduggery, and the vagaries of politics—not to mention mining—could always derail the ride.The price of gold went through the proverbial roof some time ago. Now, silver is playing catch-up. Any retailer with an Internet connection and a stake in the fine ­jewelry market could probably name the spot price of each on command. Such is the cost of doing business in a world gone mad for metals. What’s a savvy jeweler to do? It’s not easy buying or selling when the industry’s chief materials are in such financial flux; but with some key economic and industry information, it’s at least possible to anticipate where the prices are heading. The trick is to think out of the box and act quickly. Before you can do that, however, you need to understand the dynamics of the market­place. Here’s a brief