Tag Archives: die deterioration

13 Common Mint Errors of Little Value

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Machines that make coins do so with tens of tons of pressure from incredibly high-speed mass production coining presses that use brittle steel dies on all manner of planchets, some with thin-plating zinc. As working dies reach the end of their lives, or as machines rattle from all that pressure, these common errors occur on different denominations (consult the Illustrated Glossary for definitions):

  • die chatter
  • die chips
  • die cracks
  • die gouge
  • delamination
  • die dent
  • die deterioration
  • filled mint marks
  • machine doubling
  • plating blisters
  • roller marks
  • split plating
  • struck through

These are only worth a few dollars, if you can find anyone who wants to buy them. Go to the “sold” button on eBay and you’ll see the results.

Here’s some die crack examples:

How, specifically, do these errors happen?

Die Deterioration, Chips, Cracks, Gouges, Die Chatter: These occur when working dies–minting hundreds of thousands of coins–become worn from the pressure and brittle. Minute pieces of the die break or crack from the pressure, and metal fill the voids with raised appearance.

Machine Doubling, Die Deterioration Doubling, Die Dents: These are mechanical errors as opposed to mint errors. They occur when the die bounces or moves during coining. The result is not raised but shelflike.

Filled Mintmarks: Until the late 1980s, mintmarks were punched directly into the working die. This was an extra step back then, so not only do the mintmarks appear in different places but also, depending on the punch, were susceptible to clogging.

Plating Blisters, Split Plating Doubling: After 1982, cents were made of zinc. these are caused by trapped gas or thin copper plating breaking over the zinc core, often mimicking doubling.

Roller Marks: Not technically an error, these resemble the mint error on cents called “woodies” (again, consult the glossary) that look like wood grain due to improper annealing. But roller lines are caused by uncleaned rollers used in the minting process.

Delamination: This happens a metal alloy does not cohere properly, resulting in the surface peeling off. These are common in older coins, especially zinc cents.

You do not need a coin microscope to see these. Magnification makes these common errors look significant; they are not. At best these sell for a few dollars on eBay.

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You can find more information about types, varieties, errors, grading, bidding and buying in Coin News Updated: The Essential Guide to Online Bidding. Please consider buying or gifting the work for a friend, as it underwrites this hobbyist blog. Thank you.

How Coins Are Made

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If you are searching for errors and varieties, you need to know the process used at the U.S. Mint. Otherwise, you will think damaged coins are valuable errors.

Before we describe the minting process, we need to make an analogy. Most people know how newspapers are printed. So let’s start there.

Printing Process

Newsroom editors design the layout for each page, including photos and illustrations. Using a laser, a press employee creates an aluminum plate, attached to a drum. Plates are coated with ink, and the drum spins, transferring ink to rubber blanket. Paper is fed through those blankets to print each page.

If the ink blurs a page, or if there is insufficient ink, the press run has to be stopped because that error will appear in every newspaper.

This newspaper was damaged by rain and fire. It did not leave the press room like this.

Likewise, this coin was damaged by fire. It didn’t leave the U.S. Mint like that.

A damaged coin is not a mint error or variety.

The Minting Process

A coin’s design is created by artists. The Citizens Coinage Advisory Committee and the Commission of Fine Arts review designs and select one for manufacturing.

The chosen design is transferred to a master die made from hardened steel to preserve the coin for future reference. That master die creates working dies used to strike the coins. 

The Mint purchases metal coils for each denomination. Those are straightened so that the blanking press can make planchets.

Blanks are heated to soften and prepare them for striking. That process includes a striking hammer that pounds the blank between obverse and reverse of a working die.

Blanks are squeezed by a machine called an upsetting mill to form a rim. 

A quality control operator inspects the first run of a particular coin to ensure that no mistakes are made.

Mintmarks used to be hand-punched directly into the working die. Engravers manually struck a steel punch bearing the mintmark onto the die.

This resulted in varied positions and sometimes faint or shadowed impressions, known as repunched mint marks (RPMs), because a technician might not have struck the punch perfectly straight or the impression was too weak, requiring a second attempt.

Here is a nifty list so that you know how to describe the RPMs:

After 1989, the mintmark was added to the master hub, leading to consistent, identical mintmarks on all working dies from that point forward.

What This Means

Think again about a newspaper page with an error like blurred or smeared ink. Maybe one photograph with the wrong caption or misspelled name. Those errors will appear on each page unless the press operator stops the run and fixes the flaw.

This is the same process when minting coins. In other words, a particular flaw will exist on all coins made by the damaged working die.

So if you think your coin has a “unique” flaw, it is likely not an error or variety. The U.S. Mint does not make coins one planchet at a time. In fact, each die may make up to a million coins before being exchanged for a new working die.

Changing working dies means extra work. Sometimes Mint employees will polish a die so that it can continue striking. This may result in die deterioration responsible for filled mint marks, struck through grease, and “L” in “Liberty, for instance, close to the rim of a cent.

Sometimes quality control falters. For instance, some 40,000 double die 1955 cents were mistakenly released to the public. There was a reason, too. In 1955, the Philadelphia Mint was working overtime to meet the demand for new cents, primarily because of a one-cent tax on cigarettes. In the round-the-clock mayhem, the hub doubling was missed and those errors were mixed with other non-error cents.

If you understand the minting process, you won’t be led astray by clickbait social media coin videos and hyped values of error coins and varieties.

Proxiblog, operated by Michael Bugeja, a former writer for Coin World and past member of the U.S. Mint’s Citizens Coinage Advisory Committee, has seen production at the Philadelphia Mint and branch mints. He has assembled two valuable directories: one is an illustrated coin glossary that contains terms used in the minting process, and one that lists all the errors and varieties of popular denominations recognized by the U.S. Mint as well as top holdering companies.

If you like posts like this, please subscribe so you can be informed whenever there is a new article or column.

Proxiblog also has thousands of followers on Facebook Coin Groups, YouTube and social media. To get the latest discussion and commentaries, click here.

You can find more information about errors and varieties as well as buying and bidding on coins in Coin News Updated: The Essential Guide to Online Bidding. Please consider purchasing the work for yourself or a friend, as it underwrites this hobbyist website. Thank you.