Stirrup jars are made of
clay, which in unworked form occurs in beds of particles of a certain size formed from the weathering of rock. As different rocks are composed of different minerals, clay has also a certain range of compositions, all of which contain
clay minerals and sand, which is weathered
quartz. Mixed with water the particles of clay cohere in a plastic mass of loosely bonded grains. When fired, or baked in an oven, the grains indurate, or form chemical bonds between them, so that they can no longer slide over each other. Pottery is therefore constructed and shaped in the plastic phase and then placed in an oven of predetermined temperatures to cook for predetermined lengths of time. The ancients were aware of these factors and did vary temperature and time although not with today's precision. In the vocabulary of
pottery, clay pots are considered
earthenware ceramics and are typically labelled
terracotta, etymologically "baked earth". In the last few decades of the 20th century a number of questions became current about the provenance of Mycenaean pottery excavated by the
British Museum from Tell es-Sa'idiyeh in the
Jordan Valley. The pottery was Mycenaean, but was it imported or local? As a result, the British Museum's Department of Scientific Research (now Conservation and Research) decided to run a series of scientific tests on stirrup jars as representative pottery to see what determinations might be made, such as the provenance of the clay from which they were manufactured. They would perform the same tests on a "control group" of pots of known provenance in the British Museum.
Radiographic analysis The preliminary tests determined the construction of the stirrup jars by
xeroradiography, which had been adapted to archaeological images from medical technology. It produced x-ray images on paper rather than film. Like x-rays of metal castings, these images were of the masses within the border surfaces, showing cracks and inclusions. All the pots turned out to be constructed in the same way, without consideration of time or place. First the body of the pot is constructed by one of a few methods: coils, slabs or the
potter's wheel. Immediately after construction, the pot contains too much moisture to be fired, as its sudden loss would cause the pot to contract and crack. It is allowed to dry until shrinkage is complete and it reaches a state called in the trade
leather-hard, a descriptive term. Subsequently, the body is pierced and the preformed spouts are
luted (glued) in place. Etymologically the word means "mud". Lute is a
slurry of clay and other substances the potter feels would enhance the binding. The false spout may be hollow, partly hollow, or solid. If hollow, it is blocked with ceramic. Finally, the stirrup handles are luted on. Radiographic analysis revealed minor differences in construction: size and shape of the base, method of obtaining a base pot, size, shape and placement of the spouts and handles, etc. What the investigators wanted to know is whether any of these were statistically significant; i.e., were not the result of
random variation, and therefore were the signature of some potter or school of potters. They decided to perform a
quantitative analysis of each pot's elemental composition; that is, a list of elements with the percentage present. They would assume a presence of 23 elements and detect the amounts present, obtaining a profile for each pot. Software to perform an
analysis of variance of the profiles of all the samples for various factors would then detect if any factor caused a non-random difference.
Neutron activation analysis The tedious methods of qualitative analysis by chemical isolation of the components went out of general use with the invention of
mass spectrometry in the early 20th century. Most generally, mass spectrometers turn the sample into a gas (destroying it) and by bombarding it with a stream of electrons create a
plasma, or supercharged cloud of
ions, which loses the energy imparted to it by radiating wavelengths characteristic of the elemental atoms at an intensity that depends on the concentration of the element. A detector sorts the radiation by wavelength and reads the atomic spectra. Software turns the raw spectra and concentrations into a report of element and concentration present in the sample. This method was less attractive to the investigators because of sample destruction. A subsequent method activates only the
nucleus rather than the whole atom. At the British Museum, a sample powder was obtained from each jar by drilling a 2 mm diameter hole in the footing with a tungsten carbide drill. The sample was sealed in a silica tube and sent off to a laboratory. There each sample was irradiated with a stream of
neutrons. The nuclei acquired more neutrons than nature ordinarily permits, creating short-lived
isotopes, which decayed emitting a radiation characteristic of the elemental atoms, etc. The sample is not destroyed, but can be used again. Analysis of variance on the profiles of the sample jars found that minor variation of constructional features was random. On the other hand, there existed regional non-random profiles, which indicate regions of a single clay composition. The pots must have been manufactured there from them. A method had been found to identify at least by region the geological beds from which the clay had been retrieved.
Regions of stirrup-jar manufacture The control sample regions were as follows. • East
Peloponnesus, represented by 5 jars from
Mycenae and Berbati in the
Argolid, LH III A2 and LH III B. •
Attica, represented by 4 jars, LH III C. •
Aegina, represented by one jar, LH III C. •
Rhodes, represented by 3 imports from East Peloponnesus, LH III A2 and LH III B, one from Attica, LH III B - C1, and 4 native to
Ialysos, Rhodes, LH III C1. •
Crete, represented by 2 jars from
Knossos, LM III B. •
Cyprus, represented by 4 imports from East Peloponnesus, LH III A2, LH III B, and 2 native Cypriote, 12th century BC. •
Caria, represented by 1 jar from Assarlik, LH III C. •
Egypt. None were manufactured, but there were 3 East Peloponnesian imports, LH III B. In the test sample, there were • three jars from Tell es-Sa'idiyes, 12th century BC, and one 13th-century jar from East Peloponnesus. This is the first scientific data illuminating the difficult questions of who used the stirrup jars, when, who manufactured the stirrup jars, where, how they got from one place to another, and what conclusions might be drawn from their presence. Because the Jordanian stirrup jars were so late, the project confined itself to the relative time period, LH/LM III, long after the invention on Crete and introduction of the type to Greece. LH III included, however, the floruit of Mycenaean culture. Some hypotheses are evidently inconsistent, such as, stirrup jars were the monopoly of Crete and only arrived in Greece by importation from there, or that stirrup jars were moved from one area to another when they were carried there by Mycenaean Greeks. Instead, several regions of competition are defined, not necessarily as a political bloc, but as regions where the jars were manufactured locally from local clays and sold with their contents on the open market both locally and for export. There are no political implications either imperial or any other, and no ethnic implications about the exporters or importers. Anyone in the region could make and ship the pottery freely. If it was made by a royal administration in a palace, it was nevertheless sold on the free market. The manufacturers, however, as indicated by the historical documents of Linear B, might not have been free men according to today's understanding, and might not have reaped the profits. The authors do present some tentative further conclusions, dividing III into an earlier (A and B) and a later (C). In the earlier period, East Peloponnesian stirrup jars were exported to Egypt, Palestine, Rhodes, and Cyprus. In later III, Cyprus and Rhodes made their own jars, while East Peloponnesus contributed none, presumably because they did not make them any longer. The authors attribute this deficit to the destruction of the mainland palaces and the fall of Mycenaean culture there, to be replaced by Dorian. By then Jordan also was making its own Mycenaean pottery from local clays. The presence of Mycenaean pottery there is therefore not an indication that they were Mycenaean Greeks. The former Mycenaean Greeks were, so to speak, either on the defensive or on the run, faced with invasions from the Balkans. ==See also==