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When grading a coin, one of the most important factors in determining where a coin will place on the grading scale is eye appeal. Most will agree that a brilliant, fully struck, detailed coin with minimal contact marks and attractive toning is what makes for a high-grade coin.
Luster is probably the most important factor that influences a coins grade. The fine lines on the surface of the coin cause luster. As the die becomes worn, the small lines grow into larger lines that reflect less light resulting in a less lustrous coin. Light tends to reflect off those flow lines creating what is called “axial lighting”. As the light source moves the “hot spots” or areas of luster also move. This is known as the “cartwheel” effect. When evaluating a coin it’s important to rotate it under a light source to reveal whether cleaning or friction has impaired the luster. It will also allow you to check for damage or wear on the high points of the coin.
There are a number of types of luster, which result from how the dies were prepared and how they have worn. A “frosty luster” will have axial lighting that produces an hourglass shape and tends to remain in the vertical position. As the coin is rotated the hot and cool spots move giving the cartwheel effect.
A “satin luster” displays an even reflection of light. It will not display distinct axial lines or hot and cool spots. This may be referred to as a matte finish. Satin luster can result from the preparation of the dies or from dies that have not yet struck a large number of coins. As more coins are struck and the dies erode they will begin to produce coins with a frostier luster.
The “proof like” coins have a finish that is similar to proof coins. The highly reflective fields are a result of polishing the dies. The highest points of a die are the easiest to polish and this area produces the fields of the coin, which is the most reflective part of the coin. Dies are polished to remove the effects of erosion and extend the life of the die.
Keep in mind as the die becomes worn, the small lines grow into larger lines that reflect less light resulting in a less lustrous coin.
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Frosty Luster
This 1878-S is typical of coins that have a frosty luster. The hot spots show on the top and bottom of the coin. While there are some underlying reflective areas in the fields the luster on the coin is fairly uniform on both the devices and fields.
Satin Luster
The 1884-O has a very nice satin luster to it. Notice that it doesn’t show the hot and cool spots like the coin above but has an even reflection of light.
Proof Like Luster
This 1881-S has nice proof like fields with a light cameo effect on the devices. Many of the San Francisco minted coins from 1879 – 1881 will have this appearance.
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