There is no evidence of these metals being used during the time period of the Book of Mormon. So they say. Brass: Modern brass—an alloy of copper and zinc—is believed to have been invented in the sixteenth century. The Bible, however, uses the word “brass” and biblical scholars explain that this actually refers to bronze or copper. It is possible that Joseph also used “brass” to refer to bronze or copper. Other recent findings indicate that actual brass (containing zinc) was used by the Etruscans as early as Lehi’s day, suggesting that the brass plates may have actually been made of brass.
Iron: In 1996 a non-LDS Olmec specialist reported that several tons of iron had been excavated from ancient New World sites. Prior to this discovery, only a few pieces of iron were known.
Steel: When Nephi slew Laban to obtain the plates of brass, he used Laban’s own sword made of “precious steel” (1 Nephi 4:9). James H. Hunt, a critic writing in 1844, listed “steel” as one proof that the Book of Mormon was fraudulent. Hunt—who lived in the same time and general vicinity as Joseph Smith (and would likely have had access to the same resources)—claimed that Alexander the Great, who lived three hundred years after Nephi, employed iron weapons because steel was unknown. “…a coarse kind of steel, or iron carbonated,” claims Hunt, came on the scene about five hundred years after Laban and Nephi. Even as late as 1920 some critics were claiming that Joseph Smith got it wrong and that steel was unknown in Lehi’s day. Steel is typically an alloy of iron and traces of carbon that have been hardened by a process of heating and quenching. We now know, however, that deliberate “steeling” of iron was well-known in the Near Eastern world centuries before Nephi was even born. Recent discoveries, for example, include a twelfth-century B.C. carburized knife that shows evidence of quenching. An iron pick, likely dated to the same period, was discovered in northern Israel and has a hardness value characteristic with modern hardened steel. Non-LDS archaeologist Amihai Mazar, claims that this pick “is the earliest known iron implement made of real steel produced by carbonizing, quenching, and tempering.”
 Other non-LDS scholars claim that blacksmiths in the Mediterranean had mastered the process of quenching iron into weapons at least a hundred years before Nephi. Steel was likely an uncommon metal in Nephi’s world—which is probably why Nephi referred to Laban’s sword as “most precious steel”—but archaeology shows that it was not the unknown. The King James Version of the Bible often uses the word “steel” to refer to what we know today as bronze. Early societies often conflated metals. To early Egyptians, for example, copper was a type of iron. Likewise, one early New World chronicler wrote that the Tarascans (Mesoamerica’s most noted metallurgists at the time of the Spanish conquest) wore “steel” helmets. How can the Book of Mormon be faulted for using the label “steel” to refer to non-traditional steel objects if Spanish conquistadors and the Bible used the same terminology? It should also be noted that in Joseph Smith’s day the word “steel” meant “hard” or to “make hard,” and did not necessarily refer to the specific metal. Michael R. Ash, Shaken Faith Syndrome: Strengthening One’s Testimony in the Face of Criticism and Doubt