Quote:
This thread reminds me how much difficulty I have understanding AU50, 53, 55, and 58 for IHCs as well as Buffalo Nicks and Morgans. How much of the difference is degree of wear within the AU range vs. surface attributes and strike?
Here are my definitions of the AU grades with examples of early
Half Dimes. These examples are not totally perfect for the grades assigned, but they are as close as I can get using just one denomination.

AU-58 - A virtually Mint State coin with just the slightest hint of a rub on the highest. The coin should be well struck for the type. If all examples of the type are poorly struck, it might be very hard to impossible to for such coins to make AU-58. Otherwise the coin should have a minimum of marks, spots and dull spots in the luster. Ninety percent or more of the luster should be visible in the fields.
Some AU-58 graded coins are worth more to me than coins grading MS-60, 61 and even 62. This applies mostly to older classic coins that are not easily found in Mint State.

AU-55 - A nearly Mint State coin with some rub on the high points that immediately evident to the trained eye. The strike should be average or above average. More than 50% of the luster should remain, and there should be no significant defects.

AU-53 - It's been my experience that this grade is mostly applied to valuable coins that fall just short of AU-55, but have enough eye appeal to be more desirable than an AU-50. In the past this grade has been used sparingly. It's been cropping up more often of late, perhaps due to "gradeflation" which is lowered the standards for AU-50 to include the "old time" EF-45 coins.

AU-50 - Wear is quite evident on the very highest features of the design, but more than 40% of the luster is still visible. There needs to be more than just a hint of mint luster. Much of this luster is in the protected areas within the devices. The fields a usually dulled by wear. There are no significant marks or spots, although small marks can be acceptable.
A coin with attributes of a higher AU grade which has a light mark might fall into this grade. This 1794
Half Dime has a hairline scratch on the obverse which, in my opinion, lowered the grade from AU-55 to 50.
Because of "gradeflation" this coin might grade higher if I were to crack it out of its holder and resubmit it.