While gold bars are mostly uniform, there are subtle differences that can signify, among other unique characteristics, when and where a bar was cast.
Before 1986, bars cast in the United States generally were rectangular bricks. Currently, however, bars cast in the United States conform to the long-standing international standard for most bars cast overseas, which are trapezoidal in shape. For bars cast in the United States under the pre-1986 standard, a bar’s shape can also indicate where it was cast. Bars from the Denver Assay Office have rounded sides; bars from the San Francisco Assay Office have rounded corners; and bars from the New York Assay Office have square edges. Markings on the bar also reveal information about its production. For example, a set of numbers on the bar often identifies its melt—the molten gold from which a bar is made—while another set indicates its fineness or purity. A stamped seal of a refiner often identifies where the gold was cast.
Surprisingly, gold bars are not 100 percent pure gold. If they were 100 percent pure, the bars would be too malleable to preserve their shape. This would render them difficult to store or move. Therefore, each bar contains a small amount of at least one other metal, such as copper, silver or platinum. Tinges of color can indicate the type of alloy, however modest, from which a particular bar is composed. For instance, traces of silver and platinum give the gold a whitish shade, copper is most often found in reddish bars, and iron produces a greenish hue.
The market value of a gold bar depends on its weight, purity level, and the prevailing market price for gold. Rather than market pricing which fluctuates daily, the New York Fed uses the United States official book value of $42.2222 per troy ounce for gold holdings.
