Metal Inclusions in Wheat Cents, 1910 to 1919

By Shawn Tew …..
An anomaly was discovered on the obverse side of a 1912-S Lincoln Wheat cent and posted on April 13, 2019, by Joe Cronin on the discussion boards of Cointalk.com. The coin shows what appears to be chunks of brass-colored metal embedded into the surface. This led to speculations ranging from the alloys used to make the copper blanks not mixing correctly to metal falling onto the surface, possibly gold, and being rolled in.

On November 25, 2022, Blaine Neupert on his Facebook group, Lincoln Cent Coins. Rolls & Singles. Buy, Sell, Ask, Learn!, posted a 1913-S with similar gold-colored streaks on the obverse. This led to my search for other samples over the next few months. Samples were acquired of the dates 1910, 1911, 1913-S, 1914, and 1916-S, all with chunk-like metal pieces embedded onto the surface.

The sample from 1911 was different than the others, however. It had metal on the surface that resembled flakes and was not elongated like the rest. At first, the speculation was that flakes had fallen onto the surface as the ingots were rolled out into sheets. This coin had even error coin specialist Mike Diamond intrigued, and he requested to examine the coin and write an article about it that appeared in Coin World Weekly on January 30, 2023. Later, two more samples were found and acquired for study. A fourth sample is owned by Edwin Baran and a fifth is owned by Jason P. Huffman.

An initial X-ray fluorescence spectroscopy (XRF) scan was done on two samples at Liberty coin in Lansing, Michigan with the following results:

A decision was then made to have a SEM/EDX scan performed at Michigan State University’s Center for Advanced Microscopy in East Lansing.

The area chosen for the scan is marked by a box in the image; within that box, three areas were targeted.

The area labeled BASE was used for a control sample and showed normal tarnishing of a Lincoln cent. It shows a normal mixture of copper (Cu), tin (Sn), and zinc (Zn). Area two, named SPEKLE, shows us a higher-than-normal tin reading creating a Copper-Tin or Tin-Bronze alloy. Tin bronzes are known for corrosion resistance and are stronger and more ductile. The third area explored was identified as SPOT. This area gave a reading of 64.4 copper and 33.4 tin – a much higher than normal tin ratio than that found in a tin bronze. These spots are scattered throughout the flakes and act as a bonding compound, strengthening the tin bronze even more. This is believed to be the reason why the flakes retain their form and don’t elongate under pressure when rolled out for blank stamping.

We know from the 1911 and 1912 annual Mint Director’s Reports that the refinery at the Philadelphia Mint was shut down for the calendar year 1911 and blanks were purchased from an outside source. No such entity is identified in either report. Flakes are found only on 1911 cents from the mint in Philadelphia.

Other anomalies, like this 1910 below, were part of an article written by numismatist Ken Potter in 2004 and analyzed during the same scanning session. This anomaly is found from 1910 to 1919 at all three mints.

The area chosen for the scan is marked by a box in the image, and within that box, two areas were targeted. Again, the area labeled BASE was used for a control sample and showed the normal tarnishing of a Lincoln cent. The scan of this area shows a normal mixture of copper, tin, and zinc. The second sample is marked STRIPE and has a higher than normal tin reading, creating a tin bronze alloy that is tarnish-resistant.

A normal alloy mix of copper was also scanned, and two field areas were tested. The darker sample area was in line with the base results and the lighter areas once again had elevated tin readings–not as high as tin bronze but enough to resist tarnishing as much as normal copper alloy.

Also mentioned in the annual reports are the melting of old copper coins and the adding of zinc and tin for recoining. This practice is most likely the cause of alloy mix issues seen before 1958 in not only domestic but foreign copper coinage.

Article and Images ^©2023 Shawn Tew.