B. H. Roberts discusses different testimonies about the seer stones.

The sum of the whole matter, then, concerning the manner of translating the sacred record of the Nephites, according to the testimony of the only witnesses competent to testify in the matter is: With the Nephite record was deposited a curious instrument, consisting of two transparent stones, set in the rim of a bow, somewhat resembling spectacles, but larger, called by the ancient Hebrews "Urim and Thummim," but by the Nephites "Interpreters." In addition to these "Interpreters" the Prophet Joseph had a "Seer Stone," which to him was a Urim and Thummim; that the Prophet sometimes used one and sometimes the other of these sacred instruments in the work of translation; that whether the "Interpreters" or the "Seer Stone" was used, the Nephite characters with the English interpretation appeared in the sacred instrument; that the Prophet would pronounce the English translation to his scribe, which, when correctly written, would disappear and the other characters with their interpretation take their place, and so on until the work was completed.It should not be supposed, however, that this translation, though accomplished by means of the "Interpreters" and "Seer Stone," as stated above, was merely a mechanical procedure; that no faith, or mental or spiritual effort was required on the Prophet's part; that the instruments did all, while he who used them did nothing but look and repeat mechanically what he saw there reflected. Much has been written upon this manner of translating the Nephite record, by those who have opposed the Book of Mormon, and chiefly in a sneering way. On the manner of translation they have bottomed much, not of their argument but their ridicule—against the record; and as in another part of this volume I am to meet what they consider their argument, and what I know to be their ridicule, I consider here a few other facts connected with the manner of translating the Book of Mormon, which are extremely important, as they furnish a basis upon which can be successfully answered all the objections that are urged, based on the manner in which the translation was accomplished, and also as to errors in grammar, the use of modern words, western New York phrases, and other defects of language which it is admitted are to be found in the Book of Mormon, especially in the first edition.I repeat, then, that the translation of the Book of Mormon by means of the "Interpreters" and "Seer Stone," was not merely a mechanical process, but required the utmost concentration of mental and spiritual force possessed by the Prophet, in order to exercise the gift of translation through the means of the sacred instruments provided for that work. Fortunately we have the most perfect evidence of the fact, though it could be inferred from the general truth that God sets no premium upon mental or spiritual laziness; for whatever means God may have provided to assist man to arrive at the truth, he has always made it necessary for man to couple with those means his utmost endeavor of mind and heart. So much in the way of reflection; now as to the facts referred to.See Full