Doubled dies or the “doubled die” variety, is one of the most popular die varieties for collectors. Because doubled dies are so popular, there is a lot of information out there about these varieties and they are often seen for sale on internet auction sites such as Ebay. Unfortunately, not all of the information out there is correct.
A frequent misconception about doubled dies is that they are produced when coins are struck twice by the dies. This is definitely not the case. All U.S. coins made for circulation are only struck once unless there is a mishap in the coining press. Even then, the resulting error coins will NOT be doubled dies. Only proof coins are struck more than once with the number of times that they are struck depending on the alloy of the planchets that will be struck into coins. But even here, the number of times that a proof coin is struck will have no bearing on whether or not a doubled die is produced.
The key to doubled dies lies in the name – doubled die! As we have seen, coins are struck by steel rods that bear the design images for the coins that they will be striking. These steel rods are called dies. For a doubled die coin to be produced, the doubled image must be on the die itself, hence the term “doubled die.” Doubled dies occur when there are mishaps in making the dies that will be used to strike the coins.
On the “How Dies Are Made” page of this website we saw that for most of the Mint’s die making history the master design for a coin was transferred to a Master Hub in a reduction lathe. These have recently been replaced by CNC (computer numerical control) milling machines, but the principal is still the same. The master hub is then used in a hubbing press to create Master Dies. The master dies are used in a hubbing press to create Working Hubs, and the working hubs are then used in a hubbing press to create Working Dies. It is the working dies that are then used to strike the coins in the coining presses.
In the Wexler Die Variety Files we define “doubled die” doubling as doubling produced on hubs or dies as a result of a misalignment of the images on the hub and die at some point during the hubbing process. A more accurate term would be “hubbing doubling,” but the term “doubled die” is clearly fixed in our culture and here to stay. The misalignment of the design images may have been when the master hub was squeezing an image onto a master die, when a master die was squeezing an image onto a working hub, or when a working hub was squeezing an image onto a working die.
Just where the doubling occurs in this sequence will dictate how common the doubling will be, and that will affect the subsequent values for the doubled coins that are ultimately produced. Doubling can also occur in the process of transferring the design from the galvano to the master hub. Links are provided here to get more details on the doubled master hubs, the doubled master dies, and the doubled working hubs.
Since the vast majority of doubled die varieties that are reported to us are on coins from doubled working dies, that is where we will focus our attention here. Because of changes in Mint technology for making hubs and dies, the process of making a working die can be divided into two eras. These would be the multiple-squeeze hubbing era and the single-squeeze hubbing era.
Prior to the use of single-squeeze hubbing presses which could impress the complete design with a single-squeeze (hubbing), the working dies were made in multiple-squeeze hubbing presses. For the first hubbing a die blank was placed on the bottom of the hubbing chamber. A working hub was locked into the top of the hubbing chamber directly above the die blank.
Here we see the hubbing chamber of a multiple-squeeze hubbing press. Arrows point to the working hub which is locked into the top of the hubbing chamber. A die blank with the cone-shaped die face is positioned directly below the working hub. This photo is courtesy of Arnold Margolis and Error Trends Coin Magazine.
When the press was activated the working hub was lowered into the die blank with hundreds of tons of pressure. The multiple-squeeze hubbing presses did not allow a deep enough penetration into the working die to make a satisfactory impression in the working die with just one hubbing.
The working die had to be removed from the hubbing press and taken to an annealing oven where it was heat treated to relax the molecular structure and “soften” the working die so that it could receive another impression from the working hub.
This is an annealing oven that was in use at the Philadelphia Mint during a Coin World sponsored tour of the Philadelphia Mint in 1998.
When the annealing process was completed, the working die was returned to the hubbing press to receive the next impression. For the second (and later) hubbings the set-up in the hubbing press was different than that used for the first hubbing. The working die was positioned on the bottom of the hubbing chamber with the working hub sitting directly on top of it. When activated, the top of the hubbing chamber lowered and again squeezed the working hub into the working die.
This photo shows a working die (bottom) and a working hub (top) positioned in the hubbing press for the second hubbing. If additional hubbings were needed, the set-up between the hub and die in the hubbing press was the same. This photo is courtesy of Arnold Margolis and Error Trends Coin Magazine.
The hubbing and annealing processes were repeated until it was determined that a satisfactory image was on the working die. For some of the larger denominations it may have taken as many as nine or ten hubbings to leave a satisfactory image on the working die.
Since the working hub and working die were placed into the hubbing chamber manually, there was the possibility that the working hub would not be placed on top of the working die accurately. If there was any kind of misalignment of images between the working hub and the partially completed working die, doubled images would appear on the working die wherever these misalignments occurred. At this point a “doubled die” was born and if that doubled die was put into use to strike coins, all coins struck by that die would show exactly the same doubling.
After the production of the famous 1955 Lincoln cent Die #1 doubled die variety with an extremely strong spread to the doubling, the Mint took measures to prevent such widespread doubled dies from ever happening again. They placed lugs around the rim of the dies and hubs so that the images on the hub and partially completed working die would align properly when they were placed in the hubbing chamber. These lugs were raised on the working die and they were depressed indentations on the working hub.
This photo illustrates a working hub that was created for the Lincoln cent reverse. If you look carefully, you can see that the images on the face of the working hub are raised and look just like they will appear on the struck coins. The arrows point to grooves along the edge of the hub. The lugs on the working die will fit into these grooves to allow proper alignment of the working hub and the working die when more than one hubbing is needed to complete a satisfactory image on the hub or die being made.
This is a working die (left) for the reverse of the Lincoln cent as it appears after being hubbed. Notice that the design is reversed from what you will see on the struck coins. Though difficult to see in the photo, the design is depressed (incuse) in the working die. Arrows point to the raised areas (lugs) around the rim that align to the grooves of the working hub. To the right of the working die we can see some more blank steel rods that can be used to make master dies, working hubs, or working dies.
In 1969 the Mint modified the obverse design for the Lincoln cent. As a result of those changes, they experienced difficulty in getting satisfactory impressions in the working dies. To remedy the problem they removed the lugs from the hubs and dies to allow for deeper penetration of the hub into the die. This did fix the problem and allowed the deeper penetration of the hub into the die, but it opened up the possibility of doubled dies again being created with strong spreads.
It didn’t take long for the consequences of this decision to be felt. In 1969 a major doubled die was produced for the 1969-S Lincoln cents. Another major doubled die was produced for the 1970-S Lincoln cents. Several doubled dies found their way into production for the 1971 Lincoln cents with two major varieties known for the 1971-S proof cents. The dam broke in 1972 and several doubled die varieties were produced for the Lincoln cents from all three Mints including a major doubled die for the obverse of the P-Mint cents. During this period of time significant doubled dies were being produced for other denominations as well. After the flood of doubled die varieties in 1972 and all of the publicity that they generated, the Mint returned to the practice of placing the lugs around the hubs and dies.
Over the years it has been found that different types of misalignments between the images on the hub and the images on the die could occur. The various types of misalignments produced unique characteristics to the doubling found on the dies. Each identifiable type of misalignment of images produced one the “classes” of doubled die varieties. All but one of the leading die variety attributers recognize eight distinct classes of doubled die varieties. Coppercoins also uses a Class IX for doubled die varieties produced on the new single-squeeze hubbing presses. All of the other attributers feel that the doubled die varieties produced on the single-squeeze hubbing presses still fit into one of the eight previously existing classes of doubled die varieties. We have provided links to take you to separate pages for the eight classes of doubled die doubling. Each page will explain the causes and characteristics of one of the classes of doubled die doubling as well as provide you with photo illustrations of doubled dies from that class.
For more information on the various classes of doubled die varieties you can click on the following links:
When the Mint introduced the single-squeeze hubbing presses on a trial basis around 1985, and then to produce working dies at Denver and Philadelphia in 1996 and 1997, it had hoped to eliminate doubling produced during the hubbing process. Unfortunately for the Mint, this did not result and minor doubled dies are actually being produced more frequently on the new single-squeeze hubbing presses than they were on the older multiple-squeeze hubbing presses.
We believe that we know the reason for this. In the older multiple-squeeze hubbing presses the hub was fixed to the top of the hubbing chamber for the first hubbing. When it descended down into the face of the die it couldn’t move as it made contact with the die as it was locked into the top of the hubbing chamber.
In the single-squeeze hubbing presses the set up is different. The die blank is placed into the well of a collar placed in the bottom of the hubbing chamber. The hub is also placed into the well of the collar so that the face of the hub is resting on the conical point of the top of the die blank. Since the diameter of the well in the collar has to exceed the diameter of the die blank and the hub (so that the die blank and hub can be inserted into and removed from the collar, and so that the hub can be pushed downward into the die), there is “play” in the collar well. It allows for some horizontal movement between the hub and the die when the hubbing process begins. There is even the possibility of some rotational movement. It also allows for the hub to be tilted with respect to the die prior to the start of the hubbing since it is sitting unrestrained on top of the die blank in the collar well.
Since the hub is slightly tilted at the time the hubbing begins, as it is pushed down into the collar well and into the die blank it will be forced into a more vertical alignment in the collar well. If there is some resistance to the vertical realignment when the hubbing begins, it may snap back into proper alignment at some point as the hubbing proceeds. Hubbing press operators have described a “clunking sound” that is heard when the hub snaps back into proper alignment. When this happens, there will be a misalignment between the image formed prior to the hub snapping into alignment and the image formed after the snap. The result is doubling. Because the hub is not fixed to the top of the hubbing chamber as it was in the multiple-squeeze hubbing presses, the movements resulting from the “play” in the well of the hubbing chamber seem to occur frequently producing minor doubled dies.
This is a photo of a single-squeeze hubbing press in use at the Philadelphia Mint in 1998.
The hubbing press operator is placing one of the collars into the hubbing press. The die blank and working hub will be manually placed into the well of the collar prior to that start of the hubbing. The working die will be inserted first with the cone-shaped top pointing upward and the working hub will sit on top of it with the design resting on the tip of the working die’s cone.
Because of how these doubled dies are being produced, the affected area tends to be the center of the die. That is due to the fact that the point of the conical top of the die blank is the first contact point with the hub and it usually doesn’t take very long into the hubbing for the hub to snap or move into a more proper vertical alignment. While the entire obverse and reverse should always be examined carefully, the most likely place to find doubling on dies produced on the single-squeeze hubbing presses is at the center of the die (coin).
On October 1, 2009 I had the privilege of having a telephone conversation with George Shue, Senior Advisor in Manufacturing at the U.S. Mint. During this conversation the 2009-D Washington D.C. quarter with a major doubled die reverse came up. Mr. Shue noted that the Mint was aware of this doubled die error and how it occurred. This particular doubled die resulted when a hubbing press operator stopped one of the single-squeeze hubbing presses to realign the hub and die and then restarted the hubbing sequence. In the process a rotational misalignment of images resulted. Mr. Shue further noted that the Mint was able to reproduce the error in a test to see what caused the doubled image originally.
The conversation further revealed that the Mint was aware that even though it was contrary to policy, hubbing press operators were taking it upon themselves to sometimes stop the single-squeeze hubbing presses before the hubbing was completed to make adjustments, and then restarting the press to complete the hubbing. To prevent doubled dies like the major variety seen on the 2009-D Washington D.C. quarter from happening again, the Mint has installed “locks” on the hubbing presses. Now if a hubbing press operator stops the press before the hubbing is completed, they will be unable to restart the press until a supervisor comes to inspect everything to make sure that things are reset properly. The supervisor will then “unlock” the press so that the hubbing can be completed. So for now doubled dies continue to be produced despite Mint efforts to eliminate the die variety.