The Philadelphia Album reports that the plates were 7x6x6 and the sheets were the thickness of tin.

Dec 1830
News (traditional)
The Philadelphia Album

"The Book of Gold," The Philadelphia Album (Pennsylvania), December 18,1830, 405 in “The Book of Mormon,” Auburn Free Press 7, no. 29 (December 18, 1830): 2

The Philadelphia Album
The Philadelphia Album, Joseph Smith, Jr.
General Public

Upon opening this, he found enclosed a bundle of plates similar to gold, about 7 inches long, 6 broad, and in all about 6 inches deep, each sheet being of about the thickness of tin. They were united, at one edge with 3 silver wires, so that they opened in a manner similar to a book. “ They were engraven in a character unintelligible to the learned men of the United States, to many of whom it is said to have been presented. The same angel afterwards appeared to three individuals, who call themselves Oliver Cowdry, David Whitmer, and Martin Harris, and showed them the plates. To Smith was given the power to translate the character, which he was enabled to do by looking through two semi- transparent stones, but as he was ignorant of the art of writing, Cowdry and the others wrote as Smith, the person who was first directed to dig for the plates, interpreted. They say that part of the plates escaped from them in a supernatural manner and are to be again revealed when the events of time shall require them.” The book which these men have pretended to translate from these sheets of gold has been printed, and they are now busily engaged in scattering copies of it throughout the country.

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