Critics claim that gold plates of the dimensions described by the witnesses would be too heavy (on the order of 200 lbs) to be realistically lifted and carried as Joseph and others described. Thus any account involving gold plates renders the account false.

This is an example of how critics often try to confuse and mislead by making demands on what we believe. Although it is true that we use the term “gold” when referring to the plates, we have no need to believe them pure gold in order to accept the foundational history of the Church.

Many accounts refer to the plates as having the “appearance” of gold. Even those witnesses who used the term “gold” without qualifying it, were engaging in a common practice. Today we generally use the same term “gold” when referring to jewelry — chains, rings, and so on — although in practice, “gold” jewelry is almost never pure gold. Eighteen carat gold is made by an alloy process with 25% base metal content, often copper, for instance. We do not call 18k gold items “gold-copper” rings, however. Are we being deceptive because we don't?

What Were the Plates Made Of?

Were the Book of Mormon plates pure gold, or were they made from an alloy that looked like gold? The most serious investigation of this question was done 45 years ago by Reed H. Putnam of Evanston , Wyoming , a blacksmith and metallurgist. Working first from the general dimensions of the set of plates as reported by eyewitnesses, he calculated that a block of pure gold of that size would have weighed a little over 200 pounds. A number of witnesses, however, put the weight of the set at about 60 pounds. The discrepancy can be partly accounted for by the fact that the leaves must have been handcrafted, presumably by hammering, and irregularities in flatness would have left air space between the plates. This led Putnam to surmise that the entire set of plates would have weighed probably less than 50 percent of the weight of a solid block of the metal.

Because the weight of a metal depends on its purity, we must also consider whether the plates were of pure gold. The Nephites were aware of purity distinctions and alloys. We know, for example, that the "brass" plates were of an alloy (quite surely bronze, a copper-tin mixture) and that the plates of Ether were specifically distinguished as being of "pure" gold (Mosiah 8:9). Furthermore, Nephi taught his associates "to work in all manner of" metals and "precious ores" (2 Nephi 5:15). Yet nowhere does the text say that the Nephites' plates were of pure gold.

Joseph Smith's brother William specifically said that the material of the plates was "a mixture of gold and copper." (Someone must have provided an objective basis for that statement, for the natural assumption would have been that the plates were pure gold.) The cautious statements by other witnesses, including Joseph Smith himself, who spoke of the plates as having "the appearance of gold," suggest that the metal may have been an alloy.

The Tumbaga Hypothesis

Putnam observed that the only two colored metals from antiquity were gold and copper. An alloy of those two elements was called "tumbaga" by the Spaniards and was in common use in ancient tropical America for manufacturing precious objects. Putnam put forward the reasonable hypothesis that metal plates made in Mormon's day were of that material (the earliest Mesoamerican archaeological specimen of tumbaga — made from a hammered metal sheet — dates to the same century, the fifth century AD, when Moroni hid up the plates he had in his possession).

If Mormon's Book of Mormon plates were made of tumbaga, their weight would have been much less than had they been made of pure gold. Putnam made that point in mathematical detail and concluded that the total weight of the plates in Joseph Smith's charge would have been near the 60-pound figure reported by several witnesses.

It is of interest that tumbaga was commonly gilded by applying citric acid to the surface. The resulting chemical reaction eliminated copper atoms from the outer .0006 inch of the surface, leaving a microscopic layer of 23-carat gold that made the object look like it was wholly gold. Plates having "the appearance of gold," then, are exactly what we would expect if they were made of tumbaga.

Tin?

An alternative hypothesis advanced by critics, when they realize they can't stand on the “gold would have been too heavy” argument, is to fall back on the idea that Joseph made plates out of tin. There is no known evidence to support this assertion, nor does it explain how skeptical witnesses were convinced that they were made of gold, rather than tin. This accusation is interesting, because it shows how desperate some critics are to discredit Joseph Smith, yet they cannot dismiss the repeated testimony that he had actual, physical plates which many witnesses concluded were of gold, and of ancient origin.

The full FAIR wiki article, including all scriptural and academic references, may be accessed at http://en.fairmormon.org/Book_of_Mormon_anachronisms/Gold_plates.

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