*4.9. Chemical Analysis of the Bulk of the Locally Ground Yehud Coins*

The exceptional coins IAA 153976 Type 5 O1/R1 and IAA 154383 Type 5 O1/R2, having high copper content (Supplementary Materials, Tables S1 and S2, respectively), revealed different copper concentration before and after grinding.

The average copper content in the alloy of coin IAA 153976 before grinding was 27.4 ± 20.7 wt% Cu, while the average copper content in the alloy of coin IAA 154383 alloy before grinding was 22.2 ± 18.9 wt% Cu. Yet the average copper content of the ground areas of the alloy of coin IAA 153976 alloy was 32.7 ± 3.7 wt% Cu and of the ground areas of the alloy of coin IAA 154383 was 16.9 ± 6.6 wt% Cu (Supplementary Materials, Table S9). The SD of the exceptional coins was reduced dramatically after grinding the surface.

Good agreement was achieved between the surface and bulk compositions of silver coins with low copper content. For example, the average copper concentration of the alloy of coin IMJ 27424 (O1/R1, Supplementary Materials, Table S1) before grinding was 0.0 ± 0.0 wt% Cu and that of the ground bulk of coin IMJ 27424 was 1.3 ± 1.0 wt% Cu, whereas the average copper content of the alloy of coin IMJ 27383 (Type 16 O2/R2, Supplementary Materials, Table S6) before grinding was 0.2 ± 0.5 wt% Cu and that of the ground bulk of coin IMJ 27383 was 0.0 ± 0.0 wt% Cu (Supplementary Materials, Table S9).
