Tag Archives: Machine doubling

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.

VIDEO: 3 Types of Doubling

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If you want a quick refresher of the major types of doubling–hub, machine and die deterioration–view this video. It will help you identify those types with audio explanations by Michael Bugeja.

Click here for an article on the 5 types of doubling.

Also, Proxiblog has assembled some 50 videos on this site and YouTube. Click the photo below to see them.

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Proxiblog also has thousands of followers on Facebook Coin Groups, YouTube and other social media. To get the latest discussion and commentary, be sure to friend us by clicking here.

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.

3 Types of Doubling

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With the popularity of coin microscopes, hobbyists are finding all manner of doubled dies, but only one really is valuable. Nevertheless, it is important to identify the three main types so that you can tell whether you have a valuable or face value coin.

Types of doubling covered in this article:

  • Hub doubling.
  • Machine doubling.
  • Die deterioration doubling.

By becoming familiar with the various types of doubling, you not only will be able to increase your knowledge of numismatics but also can help others with their finds.

Hub Doubling

This is the most important kind of doubling, always valuable because most kinds have a decent spread of letters, numbers and devices. You usually do not need a microscope. You can see these with a loupe or naked eye.

This type of doubling is produced by a misaligned hub that engraves the defect directly into the working die, meaning the image will be evident in every coin struck by that working die. That is why the result is called a variety, and not an error.

Here is the most famous doubled die resulting from a misaligned working die:

Some 40,000 of the 1955 DDO were initially struck, with about half of the run caught and destroyed, leaving about 24,000 that made it into circulation.

The key distinction of hub doubling is separated, raised and rounded doubling. Older coins typically have this kind of doubling. In the 1990s, the US Mint introduced what is called a Single Squeeze Process, reducing the number of doubled dies with less of a spread and with doubling occurring more toward the middle of the coin.

If you want to learn more about hub doubling and the minting process, see “How Does Hub Doubling Happen.”

Machine Doubling

Machine doubling occurs when the die moves slightly during the striking process, distinguishing it from hub doubling, which is associated with the working die.

Because machine doubling happens during a strike, its “double” image is flat and shelf-like and not raised enveloping the letter or number like hub doubling,

Compare the two in this comparison image:

Machine doubling, which often requires a microscope to see, is common because the Mint uses extraordinarily high-speed machinery whose vibration often causes the working die to bounce on impact.

Machine doubling typically is caused by a single strike, meaning not all coins of that run will have the same impression, as happens with hub doubling. That is why machine doubling is a mechanical error and not a variety.

It also has no collector value.

Die Deterioration Doubling (DDD)

Like any manufacturing facility, the US Mint uses its equipment on a cost-saving basis, meaning working dies are used until they begin to deteriorate. The striking process is high-speed and powerful. When a die is overused, some of the lettering, numbering or devices begin to erode slightly with metal flows entering the degraded areas.

That’s why die deterioration doubling is common, without value, even though at times this mechanical error looks stretched rather than flat. This is how you distinguish between machine doubling and DDD. (Also, die deterioration appears to be a weak strike.)

When the US Mint started producing copper-plated zinc coins with pressure to produce billions of them each year, mint operators over-extended the lives of working dies, producing millions of DDDs.

There are two other types of doubling, “Split Plate Doubling” and “Reduction Lathe Doubling.” The former also is associated with copper-plated zinc cents with the plating eroding in what looks like doubling, especially on mintmarks that people confuse with repunched mintmarks (RPMs).

The final type is “Reduction Lathe Doubling,” really a production issue that happens when a design is transferred to a master hub by a lathe vibrating slightly. The doubling is subtle and again, not valuable. It looks like machine doubling and really is just a category of it.

If you would like to learn more about the minting process, click here.

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Proxiblog also has thousands of followers on Facebook Coin Groups and across social media. To get the latest discussion and commentary, be sure to friend us by clicking here.

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.

Machine v. Hub Doubling

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With the emphasis now on error coins, thanks in part to coin microscope sales and hyperbolic coin values on social media, it is important to know the difference between machine and hub doubling.

This is a tutorial.

Let’s start with a photo showing a machined v. hub doubled 1969-S cent. Both look significant. Only one is. Can you tell the difference? (We’ll return to these coins momentarily.)

Machine doubling, the above left photo, adds no or little value to coins. It happens when a die at the Mint begins to deteriorate and so may bounce during a strike, creating a flat shelf-like image. The date, device, lettering and mintmark can appear to be doubled.

Hub doubling, valuable, indicates a flaw in the die itself. Unlike machine doubling, which happens during a strike, someone at the Mint made an etching mistake. Mintmarks before 1989 were punched into the die; but this is distinct from hub doubling. We call these deviations “repunched mintmarks” (RPM). Hub doubling produces a raised, rounded impression that follows the flow of the date, lettering or device.

Let’s illustrate this again more closely with the 1969-S DDO cent, one of the most illusive coins, worth a bundle. It is ultra rare with PCGS holdering only 30+ coins. You can read about that here.

Clickbait social media says you can find one in pocket change. Oh, and you’ll need to buy a coin microscope for that. Fat chance.

New collectors who routinely consult social media for any number of topics often believe these hyped posts. Odds are you will never find a 1969-S DDO in rolls or pocket change. But you can find dozens of machined doubled ones on eBay and elsewhere masquerading as an authentic 1969-S DDO with sellers asking hundreds and thousands for a faux coin:

Let’s return to the images mentioned earlier and show distinctions between machine doubled and authentic doubled dies:

Machine Doubling, Left; Hub Doubling, Right

The machine doubled cent has a flat, shelf-like doubling. The doubling does not mirror the individual numbers but seem pushed to the right. The hub doubled cent has raised rounded digits that follow the contours of the numbers.

In addition to the ability to distinguish between machine and hub doubling, veteran collectors know how to identify replicas flooding the market from China. You can buy these fake ultra rarities on venues like Etsy for less than $30.

These replicas are purchased by scammers and then posted on eBay as the real deal. Now you have to compare devices with genuine coins. To do that, google a genuine one in a PCGS holder and compare doubled devices.

The obvious difference is the word “Liberty.” Take a closer look:

The doubling on the replica is mushy and below the original letters of “Liberty”; the doubling on the authentic coin is above “Liberty” with each letter mirroring the original and shifted to the right.

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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.