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Question 31
Weight of the Golden Plates

How could Joseph carry the golden plates around so easily, and how could the witness have "hefted" the plates without (a recorded) difficulty when the plates had to weigh at least 230 pounds?  (The plates are said to have been 7" X 8" X 6" high, and gold weighs 1204.7 pounds per square foot--figure it out for yourself.)

Response: by Malin L. Jacobs & John A. Tvedtnes

The critic has made three errors in the statement of his question.  When they are corrected, the problem (the perceived inability of Joseph Smith to carry the plates) disappears.

Error 1

"...gold weighs 1204.7 pounds per square foot."

A square foot of anything weighs nothing, for a square foot is a unit of area, which has no thickness.  Presumably what the critic meant to say was that gold weighs 1204.7 (actually 1206) pounds per cubic foot.

Error 2

The plates were made of 24-carat gold.

Critics fail to note that at no time does the Book of Mormon itself say that the plates on which Mormon abridged his record were made of gold.  Joseph Smith recorded that Moroni told him that the Nephite record was "written upon gold plates," but this does not exclude the possibility that they were actually a gold alloy.  Many people wear "gold" wedding bands, but they are typically made of an alloy of gold and copper or some other metal.  LDS writer Reed Putnam long ago suggested that the plates Moroni delivered to Joseph Smith may have been made of a strong alloy known to the natives of Mexico as tumbaga,1 which looks like gold, is soft enough to take the engravings, yet is hard enough to preserve them for a very long time.  Joseph Smith described the plates as

    "having the appearance of gold."2

These are the same words used by the Eight Witnesses:

    "...which have the appearance of gold..."3

If Joseph Smith, who regularly carried the plates about, and the eight witnesses, who declared that they

    "did handle [them] with our hands"4

hesitated to say that they were really made of gold, it is unwise of non-witnesses to assume they were.

Because it is an alloy of gold and copper, tumbaga is lighter than gold. Putnam concluded that the plates

    "...were probably of between 8- and 12-carat gold."5

Using the data from Putnam's article, the weight of 8- and 12-carat tumbaga can be shown to be:

    8-carat tumbaga = 0.368 lb/in3
    12-carat tumbaga = 0.603 lb/in3

Error 3

The plates were a solid block.

Unlike books printed on paper, in which the sheets lie perfectly flat against each other, the plates were first hammered and then engraved with characters.  This means that two successive plates would not be able to lie perfectly flat against each other.  Consequently, a significant portion of the volume occupied by the Book of Mormon plates was air, not metal.  Putnam concludes that

    "...the plates were manufactured by hammering the metal to a thickness of .02 of an inch with a 23-carat gilded surface of .0006 of an inch..."6

He also concluded that after being hammered and engraved

    "If each plate were .02 of an inch thick, it would occupy up to .05 of an inch in the stack."7

This means that only 40 percent of the plates' volume would be metal, with the remainder being air, which would not add to the weight.

The Dimensions of the Plates

The question under discussion estimates the dimensions of the plates as 7 inches by 8 inches by 6 inches.  Joseph Smith estimated the dimensions as 6 inches by 8 inches by 6 inches.  Other witness provided different estimates, though all of these are in the same general range.8  Joseph Smith dealt personally with the plates over a long period.  Consequently, his estimate is probably more accurate than those of the other witnesses, who saw the plates only once for a short period of time.  The 7 inches by 8 inches by 6 inches estimate given in the question results in the largest volume for the plates.  If the question can be satisfactorily answered for plates of this size, it will be satisfactorily answered for plates of the smaller size estimates.

The Weight of the Plates

Since we do not know the exact dimensions of the plates, nor do we know their exact material composition, nor do we know the precise percentage of the volume that was metal instead of air, it is not possible to calculate the exact weight of the plates.  All that can be said with certainty is that the plates must have weighed considerably less than an equivalent volume of solid gold.

The weight of a solid block of gold of dimensions given in the question is calculated as follows:

From any good physics or chemistry handbook:

    1.  1in = 2.540 cm
    2.  Weight of gold in metric units, Wgm = 19.32 g/cm3
    3.  1g = 2.205x10-3 lb

From 1:

    4.  1.00 in3 = (2.540 cm)3 = 16.39 cm3

From 2, 3, and 4:

    5.  Weight of gold in English units,
         Wge = (19.32 g/cm3)(16.39 cm3/in3)(2.205x10-3 lb/g) = 0.698 lb/in3

Now a block of gold of dimensions 7 inches by 8 inches by 6 inches has a volume of:

    6.  V = (7 in)(8 in)(6 in) = 336 in3

Therefore:

    7.  Weight of a solid block of gold of dimensions 7 inches by 8 inches by 6 inches,
         Wgold block = WgVp = (0.698 lb/in3)(336 in3) = 235 lbs.

Therefore, whatever the weight of the plates, it must be considerably less than 235 pounds.

While we can't determine just how much the plates weighed, we can come up with a reasonable estimate.  Since we have calculated the volume of the plates based on the dimensions given in the question, the procedure is to 1) multiply this volume by the percentage that represents the actual metal in that volume; this allows for the air spaces between the plates, and 2) calculate the weight based on the likely material composition of the plates.  Following this procedure yields:

From above,

    8.  Vp = 336 in3

Taking Putnam's 40 percent9 figure as the percentage of the plate volume actually occupied by metal, we calculate a reasonable estimate for the volume of the metal in the stacked plates:

    9.  Vm = (0.4)(336 in3) = 134 in3

Using the weight of the most likely range of tumbaga alloys, we obtain

    10.  W8-carat = (134 in3)(0.368 lb/in3) = 49.5 lbs

    11.  W12-carat = (134 in3)(0.603 lb/in3) = 81.0 lbs

Therefore, based on the largest estimate of plate size, they weighed between 50 and 80 pounds.  If Joseph Smith's estimate of 6 inches by 8 inches by 6 inches is used in the above calculations, the resulting weight is between 40 and 70 pounds.  Both sets of weight calculations are in good agreement with estimates made by those who hefted the plates.10

Earliest known LDS discussion:

Parley P. Pratt, Mormonism Unveiled; Zion's Watchman Unmasked And its Editor, Mr. LA ROY SUNDERLAND, EXPOSED: TRUTH VINDICATED, The Devil Mad, and Priestcraft in Danger!!!, Fourth Edition, (New York, New York: Joseph W. Harrison, Printer, 1842)

Notes:

1. Reed H. Putnam, "Were the Golden Plates Made of Tumbaga?"  Improvement Era 69:9 (September 1969): 788-89, 828-31. Hereafter referred to as Putnam. Putnam was not the first to suggest that the "gold" of the plates was an alloy of gold and copper rather than pure gold.  While not referring to the material of the plates as tumbaga, J. M. Sjodahl discussed the idea that the plates were probably made of a gold/copper alloy in An Introduction to the Study of the Book of Mormon (Salt Lake City, Utah: Deseret News Press: 1927): 43.  Hereafter referred to as Sjodahl.

2. B. H. Roberts, ed., History of the Church of Jesus Christ of Latter-Day Saints (Salt lake City, Utah: The Deseret Book Company, 1970) IV:537.

3. Book of Mormon, Testimony of Eight Witnesses.

4. Ibid.

5. Putnam: 831.

6. Putnam: 831.

7. Putnam: 830.

8. Sjodhal: 38.  It seems not to have occurred to anyone to actually measure the plates.

9. Putnam: 830.

10. William Smith and Martin Harris gave weights ranging between 40 and 60 pounds.  See FARMS UPDATE for October 1984, revised February 1985, quoting the Saints Herald 31:644; William Smith on Mormonism: 12; and Tiffany's Monthly, May 1859: 165-166.