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Coins - 1991 Proof Set Certificate of Authenticity and Coin Specifications


In the 1991 proof set, the enclosed purple card includes the coin specifications on one side and the Certificate of Authenticity on the other.

1991 Proof Set contents

At the top of one side of the purple card, the seal for the US Mint as part of the Treasury Department is on the upper left corner. To the right in bold purple letters is "CERTIFICATE OF AUTHENTICITY."

1991 Proof Set Certificate of Authenticity

The text states:

The United States Mint certifies that these proof versions of current United States circulating coinage were produced and packaged at the United States Mint, San Francisco, California. Each coin bears the mintmark “S” designation of that facility.

United States proof coins are produced from carefully selected planchets, or coin blanks, that have been burnished to a high luster. The polished blanks, which are carefully handled to minimize scratches and abrasions, are struck on specially adapted coining presses. Each coin is struck at least twice to bring forth the most minute detail with remarkable clarity.

The surfaces of the coinage dies for striking proof coins are meticulously processed to create a frosted appearance of the image on the die. The background surface is polished and buffed to a mirror-like finish. The dies are also buffed during the striking process.

The finished coin with its frosted cameo image on a mirror-like field is carefully inspected—with gloved hands to protect its surface—before being assembled into sets. The proof coins are then placed into transparent presentation cases.

Proof coins, referred to as “Master Coins” in the early days of the Mint, were originally produced to “prove the correctness of the dies.” These first pieces, struck with extra care and bearing a high polish, were reserved for the Mint’s Cabinet of Coins Collection and sometimes used for special presentations. They were first offered for sale to the public around 1858 and are produced under the authority of Section 5111 (a)(3), Title 31 of the United States Code.

Proof coins are a supplemental program of the United States Mint, produced at no net cost to the government, with profits deposited to the General Fund of the Treasury of the United States.

Donna Pope
Director of the United States Mint

The other side of the purple card enclosed with the 1991 proof set provides a table showing the specifications for each of the five proof coins in the set.

1991 Proof Set coin specifications 

The specifications include:

United States Mint Proof Coin Set







Half Dollar







Designed by

V.D. Brenner

Felix Schlag

John R. Sinnock

John Flanagan

Gilroy Roberts


Lincoln Memorial


Torch, Olive Branch, Oak Branch

Heraldic Eagle

Heraldic Eagle

Designed by

Frank Gasparro

Felix Schlag

John R. Sinnock

John Flanagan

Frank Gasparro


Copper Plated Zinc 2.5% Cu Balance Zn

25% Ni Balance Cu

Cupro-Nickel Clad 8.33% Ni Balance Cu

Cupro-Nickel Clad
8.33% Ni Balance Cu

Cupro-Nickel Clad 8.33% Ni Balance Cu

Standard Weight

2.500 g

5.000 g

2.268 g

5.670 g

11.340 g

Standard Diameter

0.750 in 19.05 mm

0.835 in 21.21 mm

0.705 in 17.91 mm

0.955 in 24.26 mm

1.205 in 30.61 mm







For further information contact:  United States Mint, Washington DC 20220  

To preserve the beauty of your proof coin set, it should be stored in a cool, dry place. 

Click 1991 Proof Set to view the contents of the proof set package.

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