Artifacts as time markers
Nails are probably the most common artifacts found on historic sites. Nails have been made in many sizes and for many purposes—from roofing to finishing. Often archeologists are able to date sites based on the characteristics of nails they recover. Hand-forged nails were the only nails available throughout the seventeenth and most of the eighteenth centuries and continued to be used well into the nineteenth century. In about 1790 the first nails cut from sheets of iron were produced. Before 1815 cut nail heads were hand-finished; after 1815 machines finished the heads. Not until the last quarter of the nineteenth century were regular sizes of round-shafted, steel-wire nails produced in sufficient quantities to compete successfully with cut varieties (NoŽl Hume 1970:253-254).
For your information
Check out Nails: Clues to a Building's History to see how nails provide one of the best clues to the age of historic buildings, especially those constructed during the nineteenth century, when nail making technology advanced rapidly.