Sieving

A technique of particle size analysis used to determine the size grades of pebble gravel, sand, and coarse silt in sediment and soils of archaeological deposits. The archaeologist processes all the earth from the site through a fine mesh, then does dry screening in a shaker frame or wet sieving with flowing water. It improves the recovery rate of artifacts. For lighter soils, dry sieving may be effective. Wet sieving is used for more claylike material and for recovering bones, shells, seeds, and other biological remains. The sieved residues are then dried and sorted by hand. The sample is placed on the top sieve of a series of nested sieves. Sieve mesh sizes are standardized. Wet sieving as part of a flotation technique is used to recover small remains from sites.

The practice of sieving soils and sediments from archaeological sites is now quite common. Sieving each bucket of spoil from the site improves recovery of artefacts, larger bones etc, which may have been missed by trowellers. A relatively coarse sieve is used for this purpose. For lighter soils, dry sieving may be effective, but more clayey material may necessitate the use of wet sieving — washing material through the sieve. Opinions are divided on the cost-effectiveness of carrying out this type of sieving on all spoil excavated from a site. Wet sieving is also a standard technique for recovering bones, shells, seeds and other biological remains for environmental archaeology studies. Large samples of spoil are removed from selected contexts on the site. These are then gently sieved under water. Mesh sizes of 2 mm, 1 mm and 0.5 mm are commonly used in sieves, the size being dependent on the remains to be recovered. Sand, silt and clay are washed through the sieve, leaving bone and shell fragments, charred material, insect skeletons etc behind, along with pebbles and gravel. These sieved residues are then dried and sorted by hand.