The main question that needs to be addressed is which factors can explain these distinct chemical signatures, supported by accurate data on a significant number of samples for each group. As of now, several possible explanations can be hypothesized, which will be further addressed in future research.
The first level of explanation we can readily suggest is a naturally occurring variation within the clayey material used, whether as a result of the use of two separate clay sources, or due to a high local chemical variation of one single source. Whatever the case, the origin of the raw material would have been discrete, since the two chemical groups are internally quite homogeneous. When examining the geochemical data, what can be noted is the fact that the observed difference does not refer to SiO2 or Al2O3 contents but mainly to K2O and CaO contents. Depending on whether this difference is related to the elements’ presence in the clay matrix or inclusions, we would interpret it differently. For example, different contents of K2O in the clay matrix might be associated with a different proportion of illitic clays in the two sources of raw materials used; in inclusions, K2O could be related to an abundance of micas or feldspars. Differences in CaO content might be associated with different natural occurrence of calcareous inclusions, but it could also originate from technological choices made by the ancient potters.
Thus, a second level of explanation relates to the technology of amphora production in the workshop and its evolution through time. Clay bodies are seldom made from a naturally occurring single source of clay sediment. Sometimes quite numerous and complex paste preparation steps are introduced in the chaîne opératoire of the ceramic product. Amphora production is generally regarded as involving minimal paste preparation since the quantities of raw materials needed to ensure a large output would be considerable. Potters are thus supposed to select the most convenient clay material available i.e. one that needs little or no preparation. Nevertheless, this rather simplistic view should not dismiss the fact that addition or removal of non-plastics and clay mixing might have taken place, sometimes in sizeable proportions, which would greatly affect chemical results. This could also explain observed differences in K2O and CaO contents.
A third level of explanation stems also from human decisions rather than from natural processes, but is related to the larger scale of economic and political spheres. It is possible that the source used at the time of Sisenna was exhausted when Domitian became the owner of the workshop or even that larger social, political or economic factors came into play—for instance, if change of ownership resulted in the availability of a new source of raw material located on imperial land. However, these hypotheses cannot be confirmed by the data so far.
For the moment, none of these explanations can be chosen with certainty above the others. However, this doesn’t mean we will not be able to elaborate more solid hypotheses in the future. When every production group will have been sampled and analyzed in the same way (totaling to at least 300 samples in the case of Loron), we will hopefully be able to reconstruct the choices made regarding raw material selection and paste preparation during the whole documented activity of at least three centuries. It will be very interesting to see if comparable patterns emerge, especially for those production groups which lie between Sisenna and Domitian. The present data also need to be supplemented with further methods of analysis, particularly dealing with the mineralogy of ceramic bodies and also by the consideration of raw materials collected in the surrounding area of the workshop.
The recipes chosen by the potters to produce those amphorae are the only remaining trace of numerous factors: choice and preparation of raw materials, the natural availability and variability of those materials, but also how the above varied through more than two centuries of recorded activity, with evidence of changes in ownership and trade of the final product. More specifically, it is interesting to investigate the effects of the shift of ownership from private to imperial status on the organization of production.
Amphorae record every step of their production and use history down to the molecular level. Thus the investigation of chemical signatures is a necessary first step towards addressing questions of fingerprinting, provenance, and technology. The question of provenance of raw materials is certainly not a trivial one in the case of Loron, since the workshop is located in a particular geological context. The Istrian peninsula is composed of Upper Jurassic to Cretaceous carbonate deposits in its southern and western part, and Cretaceous to Paleogene carbonate and clastic sequences, overlain by Eocene foraminiferal limestones, transitional beds and flysch deposits) in its eastern and northeastern part (Figure 2). Karstic and weathering processes during the Neogene and the Quaternary have resulted in the formation of different types of sediments and soils. The most noteworthy of these is terra rossa, a red soil of low calcium content, typical of the Mediterranean climate, found either in karst depressions or as discontinuous surface layers overlying the carbonate plain of southern and western Istria (called quite evocatively “Red Istria”) [3, 4]. The Loron workshop is located in this part of the peninsula and its immediate surroundings abound with terra rossa soils but lack other types of clayey sediments, especially calcareous ones, which would be compatible with the ceramic production identified in the workshop. Access to raw materials would therefore have presented a major issue for ancient potters, especially because significant quantities would have been needed to support large scale production. A similar situation is observed at Fažana, in the southern part of the peninsula. Maria Mange and Tamás Bezeczky have conducted a study of the Fažana amphorae, based on heavy minerals, which suggests that terra rossa might have been used in the production of these containers .