ROPER NEW ENGLAND SIXPENCE ANALYSIS

Figure 1. The Roper New England sixpence

When Stack's auctioned John L. Roper's New England sixpence in December 1983, it was described as "fabulous" and "the finest" of seven known specimens (Figure 1)[1]. This assessment was shared by many preeminent numismatists of the day, including John J. Ford, Jr., Richard Picker, Eric Newman, Norman Stack, David Sonderman and others and is consistent with the sharply defined and essentially pristine appearance of the stamped NE and VI impressions.

The coin recently came under scrutiny because of anomalies visible in the unstruck obverse and reverse fields that some observers believed to be plugs used to repair two small holes[2]. Detailed research and analysis will show that the anomalies were present in the hand-made planchets before striking and do not represent subsequent remediation.

METHODS
Christopher F. Pilliod, Senior Staff Metallurgist at Carpenter Technology in Reading, Pennsylvania, performed a series of physical tests on the sixpence, employing several state-of-the-art metallurgical techniques, including:

• Differential Interference Contrast Light Microscopy (DIC Microscopy).
• X-Ray Fluorescence Microprobe (XRF Microprobe).
• Scanning Electron Microscopy (SEM).

FINDINGS AND DISCUSSION
DIC Microscopy showed two distinct anomalies adjacent to one another. Figure 2 shows these at 11.4x magnification. The surface morphology of the anomalies is grossly similar to that of the surrounding unstruck field of the coin.

Figure 2. DIC Microscopy showing the two adjacent anomalies. (11.4x magnification).

XRF Microprobe is the ideal nondestructive method for compositional (elemental) analysis of a metal specimen. The silver and copper contents found in the anomalous areas and in the surrounding planchet show quite good agreement. Each is found to be composed of about 95% silver and 4% copper. As shown by previous research, these measurements are consistent with findings of Massachusetts silver coins of all series, as well as in all of the hollowware and flatware produced in the workshop of the mintmaster/silversmiths John Hull and Robert Sanderson, Sr.[3] More telling is the lead content. Lead was employed in the pyrometric refining of silver in the seventeenth century to separate it from copper. As a result, residual lead is normally found in silver coins of the period. The results showed that the anomalies and the surrounding unaffected planchet show similar silver, copper, and residual lead levels, in proportions typically found in the seventeenth-century products of the Hull and Sanderson workshop.[4] It is doubtful that such consistent results would be observed if a silver plug were placed in the setting of a modern repair.

SEM. Surface imaging with SEM yielded highly detailed images for study (Figure 3). No evidence of mechanical movement, blending, or smoothing of metal between the boundary of the anomalies and the surrounding planchet was detectable. Evidence of purposeful movement of metal would be expected in the vicinity of a plug, whether it was introduced at the mint prior to striking or done later in the setting of a repair. The absence of these findings is thus significant and constitutes strong evidence that the small anomalous areas are not plugs.

However, the strongest evidence against plugging is found in closely examining the surface topography of the coin. Note that in Figure 2, the distribution of porosity and micro-tears is uniform across the anomalies and the surrounding planchet. This is of critical importance in determining the origin of the anomalies.

Lastly, molten metal is required to create plug repairs, resulting in significant heating of the surrounding planchet. Although heating can result in microporosity or blistering, none is found in the recesses of the nearby struck area.[5] The thermal conductivity of silver is very high, and any heating for repair work would instantaneously migrate to the recesses of the nearby stamped areas. The absence of such features is further evidence against plugging.

Figure 3. Scanning Electron Micrograph. The boundary of the anomaly is indicated by an arrow. (43x magnification)

What, then, accounts for these anomalies? According to Pilliod, the most plausible explanation is that they result from small fragments of silver that never fully melted and were subsequently incorporated into the solid ingot as partially fused "inclusions." He likens the process to placing an ice cube in a glass of water and then putting it in the freezer: once the surrounding liquid solidifies, the original ice cube remains as a distinct and discernible unit within the newly frozen mass.

The differential contrast micrograph in Figure 4 is the critical image of the subject coin, proving incontrovertibly that the anomalies were produced during planchet preparation and not either as a mint-produced plug (to correct weight or surface) or as a later repair. The stark difference between the smooth topography of the stamped area and the micro-pitted area of the planchet should be noted.

Figure 4. DIC Micrograph. The anomalous areas exhibit the same microporosity as the surrounding unstruck portion of the planchet. Additionally, there is no evidence of tooling around the anomalous areas. Note as well that the recessed stamped area is smooth and shows no evidence of heating

CONCLUSION
The fact that the anomalies and the entire surrounding unstruck planchet share identical surface features and that these features are absent in the deeply struck areas proves that the anomalies were present in the planchet prior to striking and were therefore present in the coin as made. The deepest impressions of the struck areas are entirely devoid of microporosity, as the pores were entirely flattened and smoothed in these areas. These deep areas and their walls retain some original mint luster and show no evidence of secondary heating, as would be expected if a plug was introduced to patch a hole. The similar levels of residual lead in both the anomalous areas and the surrounding planchet provide further evidence that the anomalies are as made and were present in the original planchet.

NOTES:

[1] The John L. Roper, 2nd Collection of Colonial & Early American Coins, December 8, 9, 1983, Stack's, 11.

[2] Rosen, James and Anthony Terranova. 2024. "A New England Sixpence…Re-visited," C4 Newsletter, vol. 32, No. 3, 58-61.

[3] Salmon, Christopher J. 2010, The Silver Coins of Massachusetts, New York: The American Numismatic Society, 72.

[4] Note that these findings were first reported by Yale University Art Gallery curator Patricia E. Kane on page 5 and Appendix A of her 1987 Yale PhD dissertation, John Hull and Robert Sanderson, Sr., First Masters of New England Silver.

[5] Borckardt, Mark, et al. 2022. (1652) "New England ‘NE' Coinage Census," Journal of Early American Numismatics, vol. 5, no. 2, 35-114 (mentioned on pp. 40-41).

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