Archaeology Lab: Introduction to Artifacts
Artifacts are the material remains left behind by people—it is any object made, modified, or utilized by humans. From a lab standpoint, artifacts are divided into different categories: pottery, bone, lithics, metal, glass, shell, and unidentified are the usual basic categories. These categories are modified depending on the type of site you are analyzing—a prehistoric North American site will not have glass—and the preference of the lab supervisor and excavator.
These categories may be identified in the following ways:
Pottery: Pottery is any type of baked clay containing a tempering agent. Pottery is therefore made up of clay, the plastic agent, and the aplastic inclusion, or temper. Temper is something added to the clay to give the clay greater strength and to prevent shrinkage by the wet clay as it dries. Tempering agents include grit (ground up rocks), shell (ground or powdered shell fragments) and grog (ground up pottery), and organic agents (straw, Spanish moss, blood, and other things that will burn out when the pottery is fired). Without tempering agents, clay will tend to shrink and crack during drying and will fall apart quickly after baking.
From a practical lab standpoint, pottery is classified by temper and surface treatment. Potsherds are broken pieces of a pot, and are usually classified as rimsherds, necksherds, and bodysherds, depending on where on the original pot they originated. Rimsherds give the most stylistic information, as it tells quite a lot about the shape of the pot. A whole pot, should you be lucky enough to find and analyze one, is classified by rim type, surface treatment, temper, size, and shape.
Pottery is a unique substance, because it may be shaped to whatever the potter desires (within reason) due to its plasticity and flexibility. It can then be dried to increase stability and fired, at which point the shape of the ceramic cannot be altered, and the ceramic lasts almost indefinitely in the archaeological record. It therefore tells us the most about the desires of the potter who produced the ceramic. It can be assumed that all attributes of a pot were put there by the potter, although not always on purpose.
The color and surface of a pot gives information concerning
how it was fired; the shape and temper of a vessel give clues concerning its
function; consistency in vessel shape, size, and tempering give clues about how
a pot was produced and how a society is organized. Archaeologists are often obsessive about
pottery, due to the large amount of information that can be extracted from
pottery, and because so much of it appears in the archaeological record. Pottery can be distinguished from mud by its
refusal to dissolve in water and by the grating noise it gives when rubbed
against the front teeth (not to be done too often!) Different types of historic pottery can
sometimes be distinguished by the sound it makes when dropped on the table or
tapped on the teeth. Prehistoric pottery
in
Daub is a special category of semi-pottery that was originally clay tempered with grass or reeds, plastered on a structure, and allowed to bake in the sun. Normally, daub dissolves over the course of time and does not preserve; however, if a structure catches fire, daub may be fired by accident, and becomes a type of pottery. It then preserves extremely well.
Lithics: Lithics is technically any type of stone artifact. Practically speaking, however, an artifact is a lithic if it is a purposefully modified stone—fire-cracked rock (FCR) and manuported stone are traditionally classified separately, in an FCR category for the FCR, and manuports, or rocks purposefully moved into the area, are placed in a separate category such as unidentified, small finds, or rocks. Within the lithics category are two primary types—groundstone and chipped stone.
Groundstone is stone which has been shaped through pecking and grinding. The rock is usually a granite, slate, or something that will not take a point easily. Axes, adzes, and manos or metates are often, if not always, groundstone.
Chipped or flaked tools are sharp tools whose edge depends on the lack of crystalline structure of the rock. The effect is just like broken glass, with an edge much sharper than can be obtained on modern steel, as it is molecular, but which does not keep its sharpness for long periods of use. Rocks that flake or break into sharp edges are cherts, flints, jaspers, obsidian, silicified sandstone and any type of noncrystalline rock. Most projectile points and sharp tools are flaked stone—their shape depends on the fracture pattern of the raw material. Flaked stone technology is subtractive, rather than additive—the tool is made by removing material from the original core, rather than adding to the original base (pottery is additive). A good raw material for flaking often gives a distinctive “ring” when dropped on the table or tapped on the teeth. Flaked tool shapes include the projectile point, scrapers, and flaked tools. Lithics of any type can be distinguished from pottery or bone by the “hard” or ringing sound that they give when tapped on the front teeth.
Limestone and sandstone are given their own categories in most
American Bottom site inventories.
Limestone in the
Other Rock is an American Bottom site category used to describe all lithic remains that are not worked, nor sandstone, nor limestone. It tends to include manuports and mysterious pebbles that just showed up on site.
Bone: Bone is pretty self-explanatory. In some cases there may be a doubt as to whether an object is bone, lithic, or pottery. Bone almost always sticks to the tongue, due to the porosity of the bone structure. Bone itself is made up of an organic fraction, the protein collagen, and an inorganic fraction, which is the hard hydroxyapatite structure that survives longest in the archaeological record. In the initial sort, simply separating bones from other types of artifact is sufficient. In later sorts, you will want to separate out bones with cutmarks or evidence of processing, as well as bones that can be used to identify the animal it once belonged to. Teeth are particularly valuable, as they both identify the animal and age it. Bones that can be used to identify the animal are: skull elements, and any complete bones except ribs. Pieces of bone and any rib are probably not useful to the skeletal analyst. Fish, bird, and reptile bones are easily separated from mammal bones due to the different texture of the inorganic structure. Bird bones are thin and hard, fish bones are fibrous and often streamlined, and reptile bones are fibrous.
Metal: Metal is found primarily on historic sites, although not entirely. It includes iron, copper, lead, and any other metal. Bullets and rifle cartridges are often classified in a separate category, as they can be used to date a site. Iron is often encased in rust, which looks suspiciously like dirt. Some of this rust can be removed by vigorous scrubbing with a toothbrush. For further conservation of iron artifacts, you need sandblasting or reverse electrolysis.
Copper is distinguished by its green patina—this green “rust” also preserves any organic material near it. Cloth and rope fragments may sometimes be found embedded in copper artifacts, and copper should be checked carefully for this effect. Copper does not need further conservation, and the green patina should under no circumstances be removed—it protects the artifact from further breakdown.
Lead is heavy, soft, and does not corrode. It can occur in cubic crystals (galena) or shaped into bullets, plumbing fixtures, etc. Silver is rarely found. It is covered in black corrosion that may or may not be removed, depending on the eventual display purposes of the artifact.
Gold is almost never found. If it is found, you should under no circumstances tell anyone about it except as required by law, since the rumor of gold is one of the single most common reasons for an archaeological site to be destroyed by pothunters. Gold does not corrode, is heavy and soft in the pure form, and requires little conservation. Under no circumstances joke about the presence of gold in the lab—gold jokes are also one of the single most common reasons for archaeological labs being robbed.
Glass: Glass is melted silica formed into whatever shape desired by the glassblower or form. It is found exclusively on historic sites in North America, but dates back to the Old Kingdom of Egypt in the Old world. Glass bottles and vessels may be dated typologically—there is a detailed discussion of this in the Sutton & Arkush reference in the lab. Over time, water penetrates the interior of the glass, causing the glass to flake into layers. This produces the “opal” finish you often see on old glass. Left untreated, the glass will eventually break down into little flakes. Soaking the glass in ethanol or acetone for long periods of time to extract water, and then sealing with a transparent substance such as wax or glue can treat this problem.
Shell: Shell is a self-explanatory category. However, lots of information can be extracted from how the shell is worked, whether it is worked, the type of creature the shell came from, etc. In cases where a date is desperately needed, shells can be radiocarbon dated, although some fairly fancy calculations need to be made to correct for ocean carbon sink effects.