Image: Metal Bars copyright Corbis
Aside from supply and demand, one of the most basic precepts of modern economics is the concept of diminishing marginal returns. If you're hungry, your first Big Mac is wonderful. Your 10th isn't.

Diminishing marginal returns were on display Wednesday as the Federal Reserve -- as expected -- unveiled a fourth round of quantitative easing that will continue its current pace of $85 billion a month in bond purchases. But now, four years after the Fed first started expanding its balance sheets by using freshly printed dollars to buy long-term bonds, Wall Street just isn’t impressed anymore.

As a result, gold and silver got hammered Thursday on a combination of lower inflation expectations, lower economic growth expectations, and a strengthening of the U.S. dollar. By all indications, the new downtrend will accelerate from here, creating lucrative short side opportunities for nimble traders.

Silver looks to be the more vulnerable of the two metals as the iShares Silver Trust (SLV) drops out of a two-month consolidation range.

This is set to catch a lot of people by surprise. Total assets invested in the two largest gold bullion ETFs, the iShares Gold Trust (IAU) and the SPDR Gold Trust (GLD), have recently surged to new highs as people seek safety from the uncertainty of the budget negotiations in Washington, D.C.

The surge in new assets over the past two months has come despite a slow decline in gold prices, suggesting people are feeling far too good about gold and will need a serious decline to shatter the fantasy.

In response, I'm recommending short exposure via inverse exchange-traded funds (ETFs) such as the VelocityShares 3x Inverse Silver (DSLV) or the ProShares UltraShort Silver (ZSL). For individual short ideas, I've recommended short positions like Kinross Gold (KGC) to my clients. I'm adding DSLV long and KGC short to my Edge Letter Sample Portfolio.

I found these positions with the help of technical screens developed with Fidelity's Wealth Lab Pro back-testing tools, which you can find here. (Fidelity sponsors the Investor Pro section on MSN Money.)

Disclosure: Anthony has recommended DSLV long and KGC short to his clients. Be sure to check out his new investment newsletter, the Edge, and his money management service, Mirhaydari Capital Management. A two-week free trial has been extended to MSN Money readers. Click the link above to sign up. Mirhaydari can be contacted at anthony@edgeletter.c​​om and followed on Twitter at @EdgeLetter. You can view his current stock picks here. Feel free to comment below.