The United States Mint's usage of coining collars has been fairly conservative, in that few attempts have been made to go beyond the plain or reeded collars typical of our circulating coinage and most commemoratives.
The United States Mint's usage of coining collars has been fairly conservative, in that few attempts have been made to go beyond the plain or reeded collars typical of our circulating coinage and most commemoratives. An early exception was the use of a lettered collar in the creation of pattern silver dollars in 1885. These coins featured the regular obverse and reverse dies of George T. Morgan's standard silver dollar, but each coin displayed the legend E PLURIBUS UNUM in raised characters. This was achieved through the use of a segmented collar consisting of three pieces, each comprising arcs of 120 degrees. These were in a retracted position as the planchet was fed into the press, coming together to form a complete circle of 360 degrees at the moment of striking. It was necessary that they be able to retract outward after striking, because the raised metal of the edge device otherwise would have caught on the stars and lettering and fouled the ejection process.
Superintendent of the Philadelphia Mint, Colonel A. Louden Snowden, believed this segmented collar to have been his own invention, but he was proved wrong in an amusing incident related by famed coin dealer Henry Chapman. In his auction catalog for the Clarence Bement Collection in 1916, Chapman described how Snowden displayed his device to him with pride, noting that Snowden "was going to have it patented and revolutionize the World's Coinage." Chapman added that he "exhibited to him [Snowden] a crown of Oliver Cromwell, and showed him where Thos. Simon had made a better job of it 237 years before," concluding his tale with a declaration that, "The Col. collapsed forthwith."
This same type of segmented collar was again used by the U.S. Mint for circulating coinage beginning in 1907. An essentially identical edge device was imparted to all of the Saint-Gaudens double eagles, while a raised edge of 46 (later 48) stars was produced for the eagle. While these collars no doubt proved more challenging to maintain than the conventional reeded edges used previously, it was clearly demonstrated that raised lettering and other characters were practical for mass production.
After gold coinage ceased in 1933, the Mint reverted to using solid, ring-shaped collars exclusively, with their ordinary plain or reeded edge devices. Not until 1992 was anything out of the ordinary tried again. That year's commemorative silver dollar for the Olympic Games featured an edge that combined reeding with incused lettering that read XXV OLYMPIAD four times around the circumference. This was achieved in two steps: The reeding was applied by a conventional collar in the normal course of striking the coin, after which the coin was rotated within a machine that used a squeezing action to impress the lettering into the reeding. To facilitate this impression and to provide enough contrast to make the incused lettering readable, the coin's edge reeding was very narrow and closely spaced. The resulting effect was one of white lettering within a shaded background. While innovative for United States coinage, this was a technique that had been used by other nations for some years, most notably by Britain in its one-pound coins of 1983 to date.
Before leaving the subject of collars, I'd like to describe some of the more interesting mint error coins that can result when all does not go according to plan. Perhaps the most commonly seen collar-related errors are broadstruck coins. A broadstruck coin is simply one in which the collar failed to move into its proper position around the lower, or anvil, die. This permitted the planchet to expand beyond the coin's normal diameter at the moment of striking. Such coins have no edge device and may have a slightly irregular shape, though this typically is quite subtle.
Another, less common collar error is the partial collar strike, in which the collar is almost in place but does rise fully to its normal position. This produces a coin that is normal on the enclosed part of its edge and broadstruck on the remainder. The peculiar result is sometimes called a "railroad rim," as the broadstruck portion extends beyond the normally struck area in an effect suggestive of a railroad wheel's extended flange. This type of error is most visually appealing with reeded edge coins, though all variants are highly prized by mint error collectors.
Collars may be thought of as the third die in a complete set and, just like obverse and reverse dies, they sometimes display cracks and other failures. While less noticeable than on the faces of a coin, such breaks will produce areas of raised metal on a coin's edge. While obverse and reverse dies experience compression stress and have a large mass behind their surfaces to reinforce them, collars experience expansion stress and have nothing to support them. In theory, they are thus more likely to fail before producing many error coins. This could account for the rarity of mint errors confined to a coin's edge.
David W. Lange's column, USA Coin Album, appears monthly in Numismatist, the official publication of the American Numismatic Association.