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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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.
