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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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.
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.
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.
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.
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.
