It has been suggested that the golden plates discovered by Joseph Smith consisted of the New World alloy tumbaga (Putnam 1966). Since tumbaga is one of the candidates for ziff, it is appropriate to evaluate the golden plates from a scientific metallurgical perspective to see what can be determined about the plates to explore this possibility. In carrying out this analysis, it will be necessary to evaluate each merited metallurgical technique, material, or method in both the Old and New World, since a portion of the Book of Mormon golden plates was made by Nephi who originated in the Old World and traveled to the New World. In completing these comparisons, the comparison will mostly be limited to techniques known in the general area of the Middle East in the Old World, and in Central and South America in the New World. Issues of the metallurgy of Mesoamerica, where most of the credible geographic models place the Book of Mormon, will require a separate inquiry, which the author is hopeful to commence at some point in the future. That being said, there will be some general discussions included here to put the metallurgical inquiry into the golden plates in a geographic context.

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Summary

The Book of Mormon gold plates as described at the time of Joseph Smith are consistent with metallurgical properties and techniques known in the Old World prior to 600 BC and in the New World prior to AD 400, and are consistent with metal plates created to be both capable of supporting ancient engravings and to be preserved without corrosion. The ancient technologies included "black copper" patinatoin and depletion gilding. In comparison with ancient pre-Columbian gold working, the Book of Mormon gold plates could not be in the classification of the highly polished Nariño discs, but would be more along the lines of the standard polish finish exhibited on the Nariño plate work with some underlying surface relief.

Because of the description given, it was possible to determine within a narrow range the metal and alloy mixture used to manufacture the plates. If the individual plate thickness is in the thinner range of .005 inches, then the base alloy must have been copper. if the plate thickness is in the upper thickness range of 0.01 inches, then the base alloy would consist approximately of a maximum concentration of 8% gold (2 carat) with a minimum concentration of copper of 90% and silver not exceeding 2.5% and would meet the classification of the pre-Columbian tumbaga alloy. Thinner gold gilding might cause the gold content in the base metal to be up to 16.6% gold (4 carat). Based on these endpoints, the total number of plates in the entire stack was from 300 to 600.

If the base metal was copper, the gilding wound have been a diffusion gilded gold with silver impurities, with the surface of the gilding undergoing an additional depletion gilding process to eliminate the silver content in the gilding material to leave a pure gold surface. If the underlying base metal was a gold-copper-silver alloy, the surface would have undergone the depletion gilding process to leave a pure gold surface.