Accuracy of precious metals coins chief goal of Mint's assayer

Assaying team at West Point Mint tests blanks for all bullion coins
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Published : 12/16/12
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The United States Mint is committed to guaranteeing that each precious metal coin the West Point Mint produces meets the legislated standard for each issue.

Achieving that goal is the job of the U.S. Mint’s chief assayer at West Point, Jeanette Grogan, and her team of chemists, metallurgists, quality inspectors and engineers.

Grogan and her colleagues conduct the testing of every shipment of gold, silver and platinum blanks delivered by outside vendors to the West Point facility, located adjacent to the United States Military Academy in New York.

The blanks submitted by outside suppliers are intended for use to strike .9167 fine gold American Eagles, .9999 fine gold American Buffalo coins, .999 fine silver American Eagles and .9995 fine platinum American Eagles.

Grogan and three other chemists are responsible for testing samples from each shipment of blanks to guarantee they meet the legislated standards for fineness, and the stated weight of each metal as designated in the inscriptions on each coin.

“We’re actually certifying to the American public that the coins they buy from the government are the purity that we say they are,” Grogan said in a recent interview. “And we do guarantee the weight of the metal in troy ounces and the alloy composition.”

A statistical sampling is conducted of each delivery of blanks, according to standards established by the American National Standards Institute, or ANSI, Grogan said.

Grogan says she and the other chemists inspect the raw blanks as they are delivered several times a week. The universal blanks, with the proto-rims already upset, are the same whether they will be used for Proof, Uncirculated or bullion versions. (The planchets and dies used for the Proof and Uncirculated versions may receive further, special treatment to produce during striking the finish specific to each version.)

The blanks are sampled for physical dimensions, weight, diameter, surface roughness and hardness. Measurements are also taken of the thickness of the blanks, at the center and out to the edge to make sure the basin, or contour, will contribute to proper metal flow and fill of the coinage designs.

The sampled blanks are then cross-sectioned by a metallurgist to examine the grain or microstructure, Grogan said. The cross-section will then be rolled flat and sampled for alloy composition, she said.

Failure to meet established standards could result in an entire selected lot of blanks from a shipment to be rejected first, and possibly an entire shipment, Grogan said.

The top reason for a shipment of blanks to be rejected is finding blanks that are underweight, Grogan said. If a sample of blanks is found to be underweight, an additional sampling is made from the shipment before deciding whether an entire shipment will be rejected for that reason, she said.

Shipments of blanks that do meet the mandated standards are released to the production floor, Grogan said.

Grogan also oversees a team of three quality inspectors — one per shift — that examine each first strike from each pair of dies and each last coin struck from a pair of dies and perform roving inspections in between.

Each of the examined strikes is photographed, and data are archived in a permanent database, Grogan said. The documented coins are then stored in a vault at the West Point Mint.

Two engineers are part of her staff to assist with quality control and dealing with blank suppliers, she said.

A short YouTube video produced by the U.S. Mint shows Grogan and her inspection team conducting various tests. The video can be found online at http://www.youtube.com/watch?v=Hxjlj1qgQ9Y. ■

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