The earliest pottery lamps were either modelled by hand or thrown on a potter's wheel. Lamps made in a mould first appeared around the beginning of the 3rd century BC and moulding gradually replaced the earlier methods of manufacture. Unless carved in stone, the mould was taken from a patrix, a hand-fashioned model in clay or wood or another lamp. This patrix was covered in the material from which the two-part mould would be made (plaster or clay), one half at a time. Once dry and removed from the patrix, the two halves of the mould would be fired if of clay (plaster moulds were ready for use).
To make a lamp a thin layer of clay was pressed into each half of the mould and the two halves of the mould put together, the corresponding bosses and indentations of the halves providing a register. After sufficient time had elapsed for the clay to dry to a rubbery consistency, the lamp was removed from the mould. The mould seams of the lamp were then made good with wet clay and pared if necessary. The various holes were pierced where appropriate: wick-hole, filling-hole, air-hole, handle-piercing. The lamp was then left to dry out completely and fired in the kiln.
|Making the mould itself:
a) The patrix
b) Making the mould in two halves
c) Trimming the mould to shape
|Using the mould to make a lamp:|
d) Lining up the mould halves with clay already pressed inside to make a lamp
e) Opening the mould to reveal the lamp formed inside
Top half of a clay Roman lamp mould, Balkans, 2nd-4th century AD
Evidence suggests that the vast majority of Roman mouldmade lamps were produced in plaster moulds. Although relatively few moulds have survived that in itself suggests they were made of a perishable material since many thousands must have been in use over the centuries. The evidence is also on the lamps themselves: a plaster mould typically has air bubbles in the surface and a high proportion of Roman lamps show the raised globules caused by them.
Top half of a plaster lamp mould (North Africa, 5th century AD) on the left and a lamp made from a similar mould on the right.