Many critics point out that Gold Plates would have been too heavy and soft to write on. This, like so many criticisms turns out to be a straw man argument and then backfires on the critics to become evidence of the Book of Mormon’s validity.
According to Joseph Smith, the Book of Mormon was engraved on a stack of metal plates, six inches wide, six inches thick, eight inches long, and had the “appearance of gold.” Critics claim that gold plates of that dimension would weigh about 200 pounds—too heavy for Joseph to carry while running from his enemies. Those who handled the Book of Mormon, however, claim that the plates only weighed around 50 to 60 pounds. While a solid block of gold of the specified dimensions might weigh 200 pounds, unevenly hammered sheets of gold within the volume described by Joseph might only weigh 100 pounds—still heavier, however, than the weight given by Book of Mormon witnesses.
Turning to the New World we find that the ancient inhabitants did indeed make engravings on a metal which was lighter than gold but had the appearance of gold. A 1984 article in Scientific American addressed the South American discovery of several large metal objects made out of hammered sheet copper. When these copper sheets were first unearthed they were covered with a green corrosion. Once the corrosion was removed, however, it was discovered that the copper had originally been covered with a thin layer of silver or gold so that these sheets appeared to be made entirely out of silver or gold. The most important alloy discovered at these sites (and also discovered in Mesoamerica) was a mixture of copper and gold known as tumbaga. When copper and gold (the only two colored metals) are melted together they mix and stay mixed after they cool and solidify. Tumbaga ranged from 97% gold to 97% copper with traces of up to 18% of other metals or impurities. Once the gold finish was applied it would appear that the tumbaga object was made of solid gold. While tumbaga can be cast, drawn, hammered, gilded, soldered, welded, plated, hardened, annealed, polished, engraved, embossed, and inlaid it would destroy itself if not stored properly. It is therefore interesting to note that the Book of Mormon plates were laid atop two stones positioned across the bottom of the stone box so that the plates would not be exposed to water or dirt.
Too little gold in the Book of Mormon plates would have made them brittle and too much gold would have made them too heavy as well as increasing the danger of distortion during engraving. If the Book of Mormon plates were made of tumbaga, they were probably between 8 and 12 carat gold and thus would have weighed between 53 and 86 pounds. When tumbaga (which is red) is treated with any simple acid—such as citric acid—the copper in the alloy is removed from its surface leaving a brilliant .0006 inch twenty-three karat gilt coating which is easier to engrave. This process was used in ancient America. To the eye, the object would have the appearance of pure gold.
Michael R. Ash, Shaken Faith Syndrome: Strengthening One’s Testimony in the Face of Criticism and Doubt