Harris tells Tiffany that plates must have been lead or gold.
Martin Harris, in Joel Tiffany, "Mormonism—No II," Tiffany's Monthly 5, no. 4 (August 1859): 169–170.
"While at Mr. Smith's I hefted the plates, and I knew from the heft that they were lead or gold, and I knew that Joseph had not credit enough to buy so much lead. I left Mr. Smith's about eleven o'clock and went home. I retired to my bedroom and prayed God to show me concerning these things, and I covenanted that if it was his work and he would show me so, I would put forth my best ability to bring it before the world. He then showed me that it was his work, and that it was designed to bring in the fullness of his gospel to the gentiles to fulfill his word, that the first shall be last and the last first. He showed this to me by the still small voice spoken in the soul. Then I was satisfied that it was the Lord's work, and I was under a covenant to bring it forth.