This article discusses the assaying methods used by the West Point Mint.
The United States Mint is a powerhouse maker of bullion coins… there’s no bigger in the world. It takes tons of silver and gold to manufacture them. Last year alone, numbers exceeded 42.6 million ounces of silver for American Silver Eagles and neared 1.7 million ounces of gold for American Gold Eagles and American Gold Buffalos.
All the gold and most of the silver bullion coins are struck in West Point, under the helm of plant manager Ellen McCullom. The facility is among the more unique of the Mint’s four production plants. It not only makes coins like the others but it also stores gold and silver in vaults, and its lab assays precious metals to verify their fineness and quality.
To get gold for coins, the U.S. Mint buys it on the open market. This working stock isn’t ready-made for coin production since gold shipments arrive at West Point in pallets of 400-ounce bars. When needed for coinage, bars are sent to contractors for melting and molding into small discs called planchets.
Below are some of the gold planchets made by Mint contractors. Their flattened, circular shape and raised rims hint at their purpose. Planchets become coins when struck in U.S. Mint coining presses. In this photo, coin manufacturer Regina Robinson is about to do just that.
Before planchets make it to the coining press floor, West Point Mint assayers test random samples to assess whether contractors’ met their required specifications. The following photo sums up the quicker aspects of the job — studying a planchet’s visual attributes and testing its physical dimensions to include weight, diameter, and thickness. The planchets below failed.
Testing becomes more involved going forward. Queue in heavier equipment, and one of the Mint’s best and brightest — Dr. Chris Cowen, plant metallurgist. During our visit, Chris was examining the microstructure of a 0.9999 fine gold Kennedy half-dollar planchet.
This photo shows the planchet magnified, revealing its grain structure.
Another quality control device at West Point is the Wilson® Rockwell® Hardness Tester. As the name suggests, it applies precision force to determine the hardness of metals. In this case, that of a silver planchet.
Scanning electron microscopes (SEMs) find impurities in coin planchets. These next two photos are of a SEM and its image output showing trace contamination that was rolled into a gold planchet at the time of its manufacturing.
These next couple of photos cover the application of fire assay, a multi-stepped method that assayers have used for centuries because of its exacting results in finding the weight and purity of metals. In essence, the method uses chemicals and extreme heat to separate minerals and other metals from gold. (Here’s a site that does a good job in summarizing how it works.) This first photo highlights stages of the fire assay method.
Weights of the metal are taken before and after the process. The next two photos show chemist Grace Cheong cutting a pie section from a gold planchet and weighing it. The cut section is eventually rolled flat and sampled for alloy composition by fire assay.
Later in our visit, we caught up with Grace again. She was preparing microwave vessels using aqua regia to dissolve 0.9999 fine gold samples for assaying.
And here, high-temperature furnaces used in fire assay.
The next photos are of an optical emission spectrometer and a mass spectrometer. Both are used within the assay process.
Precious metals are not wasted at the West Point Mint, regardless of their form. This beaker contains dissolved gold and silver that was recovered. It will eventually get reclaimed.
Here, a photo of reclaimed gold, silver and platinum.
Before ending, our thanks go out to chief assayer Jeanette Grogan. Jeanette showed us around the lab and she also gave us our first look at 2014-W 24K Kennedy Half-Dollar Gold Coins and of 2014-W Reverse Proof Kennedy Half-Dollar Silver Coins, two of the seven coins that celebrate the 50th anniversary of the Kennedy half-dollar.
Finally, we ran across a U.S. Mint-produced video from a few years ago that features Jeanette and her team. It’s a descriptive, short piece that talks about assaying methods and their use. It also discusses other quality assurance measures that the West Point Mint has implemented. We’ll cover them in more detail in a later article. Here is the video:
That’s it for this article. As always, thank you for stopping by. Check back soon for another piece about the West Point Mint.