by Ken Camilleis

Using my method of mapping the CGI into RD/RB/BN, I have developed a net grading system for copper somewhat similar to EAC’s approach but making use of the AU range of Sheldon numbers (50-59 including the increments not presently used in the coin market) to further dissect the mint-state range based on how the coin would color-grade with respect to the CGI. This system superimposes the AU range numbers of 50 through 59 with “MS” designations, and is a good guide for the marketability of a mint-state copper. For RD coins, the CGI grade is equal to the slab grade, but for RB and BN coins, the conversions tabulated are as follows:

        Slab Grade    CGI Grade      Market Grade
MS60BN         MS50           AU50
MS60RB         MS51        AU53
MS61BN         MS51           AU53
MS61RB         MS52           AU55
MS62BN         MS52           AU55
MS62RB         MS53        AU58
MS63BN         MS53        AU58
MS63RB         MS54        MS60
MS64BN         MS54        MS60
MS64RB         MS55        MS61
MS65BN         MS55        MS61
MS65RB         MS56        MS62
MS66BN         MS56        MS62
MS66RB         MS57        MS63
        MS67BN         MS57        MS63
        MS67RB         MS58        MS64
        MS68BN         MS58        MS64
        MS68RB+         MS59        MS65

Using this table, say you have an 1820 large cent that slab-grades MS64BN. Chances are that it is on or near the low end of the CGI spectrum, known as “CGI-7”, or it may be something like “CGI-6.5”. Its CGI grade would be “54” and its market grade would be MS60. However, if the luster on the coin was unbroken and the color was not the typical tarnish of brown, its CGI rating would be considerably higher such that it is marketable as a RB. This would translate to an MS61, or, better still, if the CGI rates the color/luster at 4 or smaller, it qualifies as a “RD” and repre-sents an actual 64 value! Note that the number “54” is an indexed conversion, which means that since the Sheldon MS grades of 60 to 70 are reserved for RD coins with respect to EAC and CGI grading, this is about an average mint-state coin in terms of contact marks or carbon spotting. For RB and BN coins that would net-grade mint state, we use what I refer to as the “Rule of 6” by computing the CGI grade and adding six to get the net “MS” market grade.

One important principle of the CGI is that although it runs from 1 (fresh, untoned as it came from the Mint) to 7 (fully brown, unworn with minimal luster), it is not merely seven points on a scale but a continuous spectrum of values. As the three designations of RD, RB and BN are really too limited in describing toning on coppers, there is much subjectivity when color-grading coppers. The CGI not only bridges opinion gaps but also clearly defines a method for intelligently figuring color and luster into the net marketability grade of a copper. It is especially noteworthy that mint-state coppers can have heavily contrasted colors from obverse to reverse, and the CGI is really the average of a dual grade for both sides (e.g. CGI-2.5/CGI-4 = net CGI-3.25).

While there will be coppers that do not evaluate exactly as defined in the above tabula-tion, this analysis is based on personal examination of thousands of high-grade coppers.