Terracotta oil-lamps were used as a source of light by almost all ancient civilisations, offering an alternative to candle light. Candles, made from beeswax or tallow, were of course cheaper to buy but did not last that long. Oil-lamps generally functioned by pouring oil through a central hole and burning a wick placed into the nozzle area. Wicks were commonly made from pieces of linen but were also made from flax or papyrus. Pottery oil lamps were made in three different ways: hand-crafted, wheel made, or made with the aid of a mould. The use of moulds became increasingly popular, as once made, a mould could be used to create a number of lamps, which meant that lamps could be easily and directly reproduced. This method also ensured that the manufacturing of lamps could be extremely efficient and organized manufacturing and also a fairly lucrative one, producing large volumes of goods with a standardised quality. Moulds were made from either clay or plaster. Roman lamp makers preferred the use of plaster moulds but both types had advantages and disadvantages. For example, a clay mould would require firing whereas a plaster mould could be left to dry. However, plaster moulds also wore out quickly, as the surface would deteriorate through repeated use. It is possible to determine whether a lamp was made with the use of a plaster mould, as such moulds would often contain air bubbles, created during its manufacture. These air bubbles would create visibly obvious raised bumps which were subsequently pressed into the clay. To use a mould, clay would be pressed into both halves, with any extra clay cut off at this point. The maker would then press the two sections together and leave them to dry. Once dry, the two sections of the mould would be removed. Where the two pieces of clay met, wet clay could be added to ensure the join was neat. Also at this stage, the required holes would be pierced into the clay. These holes could become the filling hole, the wick hole or an air hole. A handle could also be added if this had not been part of the main body. The lamp would then be left to air thoroughly before a glaze could be applied and finally the lamp could be fired.
A simple and early form of lamp was the cocked-hat type. This was created by producing a shallow bowl or plate and folding in the edges whilst the clay was still wet. Many fired clay lamps came in basic shapes, with round or oval bodies. In addition to these, more elaborate lamps could be found, in the shapes of animals and imitating parts of the human anatomy. Other variations in style could include the number of nozzles. Lamps with several nozzles could hold several wicks, thereby producing more flames and more light. Levels of decoration on lamps could vary enormously, and depend upon the date of manufacture but also upon limitations created by the shape and size of the lamp itself. Some lamps contained a large central circular area which contained the filling hole. This area allowed space for decoration, with scenes ranging from everyday activities, to entertainment such as gladiatorial scenes, to depictions of common myths. In addition, more simple decoration could be added through the use of raised circles and dots around the central hole. Glazes were often applied to lamps of Roman origin. Although these glazes could contribute to the final colour of the pot, they were not generally used for decorative purposes. Instead they served a useful function, as the addition of the glaze ensured that the lamp was more watertight. Most glazes used were in fact simple slip coverings, washed on to the pot and would vary with the location of lamp manufacture, as did the clay itself used for the construction of the main body of lamp. They could be applied by painting on the slip, pouring the slip on the lamp, or by dipping the lamp. This dipping technique often could result in lamps with finger marks, showing where they were held during this process. Plain and undecorated lamps would be cheaper to produce and in consequence to purchase, these simpler types of lamps are more often found in military zones of the Roman empire. Pottery lamps are extremely useful finds on archaeological sites. Due to the ability to date pottery through closely studying the material, styles and material of lamps, archaeologists are able to gather much information about them and other finds. As clays varied depending upon the location, a lamps appearance could also vary. By looking at the colour, texture and the presence of any grit in the clay, archaeologists are able to assess where the lamp was produced. They also allow an insight into the culture of the empire, and through their different styles allow a glimpse into the social status of the users.
This elegant seven wick red-slipped Roman oil lamp has the sunken discus decorated by a number of concentric circle, in turn decorated by short radiating lines, with a central filler hole.