Evidence #76 | September 19, 2020

Composition of the Plates

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Scripture Central


The reported weight and appearance of the metal plates of the Book of Mormon can be adequately explained if they were made from a gold alloy called tumbaga, which was commonly used in ancient America.
Eight Witnesses View the Book of Mormon by Dale Kilbourn

A number of historical documents contain reported descriptions of the weight, appearance, and dimensions of the metal plates from which the Book of Mormon was translated.1 From these descriptions, researchers with relevant expertise have attempted to identify the material composition of the plates.

In 1966, blacksmith and metallurgist Reed H. Putnam suggested that the plates were possibly made from an alloy called tumbaga,2 which was commonly used in South and Central America and consists of copper, gold, and sometimes silver.3 If the plates of the Book of Mormon were made from tumbaga, it may help explain why some witnesses described them as only having the “appearance of gold”4 and why William Smith reportedly stated that they were “a mixture of gold and copper.”5

Plates made of pure gold would have been very heavy, possibly about 100 lbs.6 Yet, according to Putnam, if the plates were made of tumbaga they might have only weighed about 53 lbs, a much more manageable weight for hefting or carrying them over any significant distance.7 More recently, geologist and engineer Jerry Grover has analyzed several possible combinations of gold, copper, and silver, based on varying estimates for the thickness of the plates. He found two plausible scenarios that would respectively place the plates’ weight at approximately 54 and 58 lbs.8 These estimates accord with descriptions made by those who hefted the plates for themselves, which ranged between 40 and 60 lbs.9

Comparison of tumbaga vessel with a more reddish copper color and a tumbaga bird firgurine with a more golden finish. Featured left: gold and tumbaga vessel from Sicán culture, Peru, 750-1375 Pre-Columbian; Birmingham Museum of Art. Featured right: Pre-Columbian "birdman" made of tumbaga, from the Smithsonian.

While tumbaga is naturally a reddish color, its exterior was commonly made to look golden by leeching out the copper on the surface. One method of accomplishing this involved the application of “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.”10 This process and several others were commonly used in pre-Columbian America.11

On one occasion, Josiah Stowell reportedly saw a small corner of the plates when part of the frock Joseph Smith had used to cover them slipped off. Stowell said the plates “resembled a stone of a greenish caste.”12 This otherwise inconsistent report about the color of the plates might be adequately explained if the plates were made of tumbaga. It is possible that over time some of the gold gilding on the edges of the plates had worn off and the copper underneath had begun to oxidize, which would naturally turn them a greenish color.13 

Tumbaga makes sense for other reasons as well. Pure gold would be too soft, and thin plates of pure gold would not hold up well. The large quantity of copper in tumbaga makes the alloy more rigid and resilient, even in thin sheets.14 Furthermore, the thin gold surface that remains after a gilding process would have made the plates easy to engrave, while at the same time protecting them from rust and corrosion.


Image and description from "Of What Material Were the Plates?" Journal of book of Mormon Studies 10, no. 1 (2001): 21.


While it is impossible to know the exact composition of the plates, tumbaga is a very appealing possibility. Not only does it adequately explain the reported weight and appearance of the plates, but it is known to have been used in ancient America, including Mesoamerica where many scholars believe the recorded narratives in the Book of Mormon primarily took place.

Book of Mormon Central, “What Kind of Ore did Nephi Use to Make the Plates? (1 Nephi 19:1),” KnoWhy 22 (January 29, 2016).

Jerry D. Grover Jr., Ziff, Magic Goggles, and Golden Plates: The Etymology of Zyf and a Metallurgical Analysis of the Book of Mormon Plates (Provo, UT: Grover Publishing, 2015).

Kirk B. Henrichsen, “How Witnesses Described the ‘Gold Plates’,” Journal of Book of Mormon Studies 10, no. 1 (2001): 16–21.

Of What Material Were the Plates?” Journal of Book of Mormon Studies 10, no. 1 (2001): 21.

Robert F. Smith, “The ‘Golden’ Plates” in Reexploring the Book of Mormon: A Decade of New Research, ed. John W. Welch (Provo, Utah: FARMS, 1992), 275–277.

Reed H. Putnam, “Were the Golden Plates made of Tumbaga?” Improvement Era 69, no. 9 (September 1966): 788–789, 828–831.

The Testimony of the Three WitnessesThe Testimony of the Eight WitnessesThe Testimony of the Prophet Joseph SmithMormon 6:6Mormon 9:35Ether 5:2

The Testimony of the Three Witnesses

The Testimony of the Eight Witnesses

The Testimony of the Prophet Joseph Smith

Mormon 6:6

Mormon 9:35

Ether 5:2

Records and Relics
Book of Mormon

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