Assaying Gold at the West Point Mint

by Mike Unser on August 29, 2014 · 1 comment

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.

West Point Mint Assaying

A few West Point Mint employees and assaying devices

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.

Gold Bars at West Point Mint

Some of the West Point Mint’s working gold inventory. These 28-pound .9999 fine gold bars are in storage, waiting for gold coin production.

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.

Regina Robinson, Coin Manufacturer at West Point Mint

Regina Robinson, Coin Manufacturer at West Point, selects gold planchets from a tray. Each is manually inserted into a coining press to strike Kennedy 50th Anniversary gold coins

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.

Examples of planchets with burrs, missing upset, spots and low weights

Examples of planchets with burrs, missing upsets, spots and low weights

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.

Dr. Chris Cowen, Plant Metallurgist at West Point Mint

Dr. Chris Cowen, Plant Metallurgist at West Point Mint

This photo shows the planchet magnified, revealing its grain structure.

Magnified cross-section of Kennedy gold planchet

Magnified cross-section of a 50th Anniversary Kennedy gold planchet

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.

Hardness tester at West Point Mint

Hardness tester at West Point Mint

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.

Scanning Electron Microscope (SEM) with Elemental Detection System (EDS)

Scanning Electron Microscope (SEM) with Elemental Detection System (EDS)

Data output from the SEM and EDS

Data output from the Scanning Electron Microscope (SEM) and Elemental Detection System (EDS). The streak is a slight amount of silver that shouldn’t be present in gold planchets.

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.

Photo of the fire assay method

Photo 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.

Grace Cheong, Chemist at West Point MInt, weighing 0.9999 fine gold

Grace Cheong, Chemist at West Point Mint, weighing 0.9999 fine gold

Gold planchet, cut

Gold planchet, cut

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.

Grace Cheong, Chemist at West Point Mint - Preparing microwave vessels

Grace Cheong, Chemist at West Point Mint – Preparing microwave vessels

And here, high-temperature furnaces used in fire assay.

Furnaces at West Point Mint used for the assaying of gold blanks

Furnaces at West Point Mint used for the assaying of gold planchets

The next photos are of an optical emission spectrometer and a mass spectrometer. Both are used within the assay process.

Inductively Coupled Plasma - Optical Emission Spectrometer (ICP-OES) instrument

Inductively Coupled Plasma – Optical Emission Spectrometer (ICP-OES) instrument

Inductively Coupled Plasma - Mass spectrometer (ICP - MS)

Inductively Coupled Plasma – Mass spectrometer (ICP – MS)

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.

Photo of dissolved gold and silver

Photo of dissolved gold and silver

Here, a photo of reclaimed gold, silver and platinum.

Reclaimed silver, gold and platinum from the assaying process

Reclaimed silver, gold and platinum from the assaying process

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.

Jeanette Grogan, Chief Assayer, West Point Mint

Jeanette Grogan, Chief Assayer of the U.S. Mint, holds a recently produced 2014-W Reverse Proof Kennedy Half-Dollar Silver Coin.

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.

{ 1 comment… read it below or add one }

Eric August 30, 2014 at 3:22 am

Great series on the West Point Mint!

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