Portuguese Mint develops new technology for off-center coin

‘Eccentric’ coin blends history, technology
By , Coin World
Published : 10/19/14
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Editor's note: The following is the second of a two-part Coin World series about the blending of history and technology in a new collector coin from Portugal, prepared by Jeff Starck for the November 2014 monthly edition of Coin World.


Mint officials have been somewhat reserved when asked about the technology behind the "eccentric" coin, declining to provide more than basic answers about how the coins were made.

A short video about the coin shows some of the tooling being created, and it’s possible that mint officials are content to let the coin do all the talking.

This new bimetallic coin and the process to produce it with only one coinage operation (which is patent pending) was developed by the mint beginning in 2013, and overall took 18 months to refine, Verdasca said.

The eccentric coin required specially prepared dies and collar to enable the mint to strike both pieces of the coin together, at the same time, ensuring the link between both metals.

“The off centered inclusion of the gold blank, the particular non round shape, and the different sides of the coin suggested the obvious: [it] is really an eccentric coin,” Verdasca said in an email.

The .925 fine silver blank has a diameter of 28 millimeters, and the .999 fine gold blank measures half that, 14 millimeters in diameter.

Based on images provided by the mint, it is evident that a portion of the silver blank was removed to create a cavity, or nest, for the gold blank; then both pieces were melded together during the striking process.

The entire gold disk is visible on the obverse side of the coin, while only the small portion projecting from the larger silver disk is visible on the reverse.

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