Learn Grading: What Is a Mint Error? — Part 3

Every year, mints for major countries produce billions of coins. Despite sophisticated technology and comprehensive quality control efforts, some mistakes are made. Coins with mistakes are called “mint errors” and are among the most popular segments of numismatics.

In this series, NGC continues to explore mint errors and their causes. Part 1 focused on the mint errors primarily caused by the dies used to strike the coins, and Part 2 began to look at errors caused by the strike itself. Here in Part 3, we continue to look at strike issues.

Broadstrike: A broadstruck error occurs when a coin is struck without the collar to form the rim and edge that is part of the shape of the coin.

1968 India 3 Rupees, Broadstruck Click images to enlarge.

Partial Collars: Partial collar strikes occur when there is a malfunction of the striking press. This causes the collar to be in an incorrect position. The lower die is recessed in the collar. This allows the coin which is going to be struck to have a formed rim. After a coin is struck the lower die raises upwards, pushing the struck coin out of the collar and ejecting it. If a blank entering the collar is not properly seated, it will only have partial reeding as it is struck. The edge of this coin will have a partial reeding and a partial blank surface area.

This 2015 India Rupee has two mint errors: a large obverse cud, as well as a partial collar. A partial collar occurs when the collar that holds the coin and prevents it from speading out past the confines of the die doesn’t fully engage. This leads to a slightly out-of-shape planchet, which is most easily seen at 9 o'clock on the reverse of this piece. The edge is left with a distinctive “railroad rim” look as well. Click images to enlarge.

Brockages: A brockage error can only occur when there are two coins involved. One of the coins involved will always be a struck coin which has not ejected properly. That struck coin will find its way back between the dies and will be struck next to a blank planchet which was fed into the collar. The image of that first struck coin will be impressed into that side of the blank planchet. The result will be a second coin that has images of the first coin impressed into it. Those images will be pressed into the coin and the image will be in reverse. This incuse sunken image is known as a brockage.

1938 Egypt 10 Milliemes, Brockage on Reverse, NGC AU55 Click images to enlarge.

Die Caps: A die cap is caused when a struck coin sticks to one of the two dies. Once the coin is stuck to the die, the reverse of the normally struck coin essentially becomes the new die face. When the next blank is fed into the collar and the strike occurs, the reverse design of the adhered struck coin impresses itself into the new blank. This struck coin is a brockage strike. The coin that is adhered to the upper die is known as a die cap. This process repeats itself as more coins are struck by the cap. The greater the number of strikes, the higher the metal will be pushed around the upper die shaft, creating the capped shape.

1964 Great Britain 3P, graded NGC Mint Error MS 65 – Obverse Die Cap Click images to enlarge.

Counterbrockages: A counterbrockage error involves a capped die and a previously struck coin. When a cap die strikes a previously struck coin, the obverse design from that struck coin will be impressed into the cap. The result will be a design where the cap face will be an incuse brockage. When a new blank is struck by this cap die with an incuse brockage image, the obverse will have a raised and spread image from that incuse design of the cap. This brockage impression is known as a counterbrockage.

Undated Indian Cent (1859-1909), graded NGC Mint Error MS 65 BN, with Obverse Counterbrockage. As is typical of a counterbrockage, certain design elements are missing—in this case, near the obverse’s rim, including the year and the words UNITED STATES OF AMERICA. Click images to enlarge.

Bonded Coins: Bonded coins are created when the feeder system, which supplies blank planchets to the coin press, malfunctions and jams. When this occurs, a struck coin is not properly ejected and another planchet is fed into the collar and is struck. This struck coin will land on top of the previously un-ejected strike. These coins will then crush and bond together. This may happen multiple times as more coins bond, resulting in extremely dramatic errors.

1964H East Africa 10C, graded NGC Mint Error MS 64 RB – Bonded Pair and Struck Three Times. Click images to enlarge.

Mated pairs: Mated pairs involve two individual coins that were struck together at the same time. Mated pair error combinations can be found in most error types and come in many shapes and sizes. Mated pairs can be overlapped when one of the coins is struck off-center on top of another coin. Another type involves a brockage where a struck coin was perfectly centered on a blank and re-struck. Some mated pairs involve a die cap where the cap and brockage coin are discovered together, but this is a scarce find. Mated pairs can also involve an off-metal error, in which a smaller blank planchet or smaller struck coin was struck on top of a larger coin. This type is extremely rare.

Two 1998 Quarter planchets graded NGC Mint Error MS 63 and 66 – Mated Pair. They were struck together, and most of the strike hit the first coin. A small part of the design was imparted to the second coin. Click images to enlarge.

Double Denominations: One of the most popular and desirable types of errors are double denominations. This error happens when a coin is struck on a previously struck coin of a smaller denomination. Examples are a cent on a struck dime, and a nickel on a struck cent. The most dramatic are those with considerable design visible from the original strike. There are a few known double denominations with different dates.

1990 Great Britain 20P Overstruck on 1990 New Zealand Dollar, graded NGC UNC Details - Cleaned Click images to enlarge.

NGC attributes major mint errors under its Mint Error service for an additional fee. For more information about NGC Services & Fees, click here.

Related links

• Learn Grading: What Is a Mint Error? — Part 2
• Learn Grading: What Is a Mint Error? — Part 1
• Learn Grading: What Are the SP and PL Prefixes?
• Learn Grading: What is a Proof Coin?
• Learn Grading: What is an NGC Details Grade?
• Learn Grading: What Are the Plus and Star Designations?
• Learn Grading: What Are Full Bell Lines?
• Learn Grading: What Is the Full Head Designation?
• Learn Grading: What Are Full Bands and Full Torch?
• Learn Grading: What are 5FS and 6FS
• Learn Grading: What are BN, RB and RD?
• Learn Grading: Prooflike (PL) and Deep Prooflike (DPL)
• Learn Grading: Proof, Proof Cameo and Proof Ultra Cameo