Henry Caswell reports Lucy Mack as describing Joseph translating the BOM through using the Urim and Thummim resembling two large diamonds in a pair of spectacles.

"The angel of the Lord appeared to him fifteen years since, and shewed him the cave where the original golden plates of the book of Mormon were deposited. He shewed him also the Urim and Thummim, by which he might understand the meaning of the inscriptions on the plates, and he shewed him the golden breastplate of the high priesthood. My son received these precious gifts, he interpreted the holy record, and now the believers in that revelation are more than a hundred thousand in number. I have myself seen and handled the golden plates; they are about eight inches long, and six wide; some of them are sealed together and are not to be opened, and some of them are loose. They are all connected by a ring which passes through a hole at the end of each plate, and are covered with letters beautifully engraved. I have seen and felt also the Urim and Thummim. They resemble two large bright diamonds set in a bow like a pair of spectacles. My son puts these over his eyes when he reads unknown languages, and they enable him to interpret them in English. I have likewise carried in my hands the sacred breastplate. It is composed of pure gold, and is made to fit the breast very exactly."See Full