**1. Introduction**

The exploitation of molluscs providing the fabulous purple dye (in Greek, porphyra = πoρφ*υ*´ρα) in the Prehistoric Aegean, as evidenced by archaeological research, illuminates many aspects of the societies that developed it and bequeathed it to subsequent civilizations. The production at a commercial scale of "true purple" dye, obtained from the secretions of shellfish species native to the Mediterranean Sea, had a significant social and economic impact in the Aegean Bronze Age. Dyeing seems to have been an integral part of the production and distribution of textiles, whereas the extraction and the application process of the purple dye, demanding exceptional skills and much know-how, was presumably a preserved secret among the guild of specialized experts. The impact of the murex dye industry in the ancient Mediterranean societies was related to the value of dyed garments and colored textiles in general as symbols of social status and power, with the shellfish purple dye representing an added value and denoting the highest societal rank in many cultures around the Mediterranean basin during the Bronze Age and far later on [1,2].

Although the earliest record for the purple dye comes from inscriptions on the Mycenaean Linear B clay tablets dating to the 13th century BC, where the term "royal purple"

**Citation:** Sotiropoulou, S.; Karapanagiotis, I.; Andrikopoulos, K.S.; Marketou, T.; Birtacha, K.; Marthari, M. Review and New Evidence on the Molluscan Purple Pigment Used in the Early Late Bronze Age Aegean Wall Paintings. *Heritage* **2021**, *4*, 171–187. https:// doi.org/10.3390/heritage4010010

Received: 19 December 2020 Accepted: 11 January 2021 Published: 14 January 2021

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(Knossos X 976) was probably mentioned for the first time [3], important shell deposits of gastropods of the Muricidae family have been studied and confidently attributed to a non-dietary use of molluscs far earlier. Heavily fragmented shell debris in a primary production context or concentrations of crushed murex in a secondary use context are considered evidence of purple dye production activity at many Aegean sites, dating mainly from the Middle and Late Minoan periods, and in certain cases from the Early Minoan period [4]. The early archaeological evidence of the purple industry around the Mediterranean Basin is significant in both the Aegean and the Levantine littoral [4–9]. The question of whether the secret of the purple dyeing process and its exceptional properties was first discovered in the Aegean or the Levant has yet to be resolved, but given the established trading relations between the Aegean and the eastern Mediterranean coasts in the middle of the second millennium BC, it is reasonable to suggest that the process of extracting a commercial dye from murex species may have been practiced contemporaneously in many of the important Eastern Mediterranean centers, where familiarity with marine molluscs is evidenced by the shell middens, as well as by shells found in second uses (mortar, etc.) [10].

The chances of finding the proper product of the purple dyeing industry, a purpledyed textile, decrease geometrically as we go back in time. However, residues of dyed textile, in which mollusc purple is identified, date back to the Late Bronze Age. In present evidence, the earliest cases belong to archaeological sites in Syria. Purple-dyed textile fragments were found first in a royal tomb complex in the Bronze Age palace of ancient Qatna, Tell Mishrife, Syria, discovered during excavations in 2002 [11]. It is estimated that the tomb was used for 300–400 years for the burial of kings, prior to the destruction of the palace by the invading Hittites in 1340 BC, a date that is extremely early given the fragility of the fiber substrate. Brominated and non-brominated indigoid compounds of a similar composition were identified in purple-colored extracts both from fragments of woven fabrics and samples in brown-stained areas of the layer of sediment covering the tomb floor, from which it was concluded that the colorants present in the sediment extracts were residues of the purple used to dye the royal fabrics [12]. Then, in a more recent excavation, shellfish purple-dyed textile residues dating to the 18th–16th century BC were identified in Chagar Bazar [13]. This earliest direct evidence of purple-dyed textiles confirm the early dating of the purple-dyeing industries at the coastal Levantine sites in Syria (Minet el-Beidha/Ras Shamra) and in Lebanon (Sarepta), so far documented only through the studied heaps of murex, as well as the identified purple substances on shreds of jar-type vessels with purple sediment in their interiors [7,10,14–17].

Another direct piece of evidence for the shellfish-purple dyeing industry raised from an excavated complex alluding to a dyeing installation is provided by containers that preserve purple traces, analytically proven to contain indigoid compounds [1,18]. One of the earliest instances of such purple-stained vessels with crushed shells, which dates back to the Middle Minoan period, MM IIB, was found at the site of Pefka, near Pacheia Ammos, on Crete [19,20].

A third, equally strong direct piece of evidence for purple production is the identification of the pigment prepared for use in painting; we are referring to the *purpurissum*, according to Pliny the Elder and his vat-dyeing recipe [21]. The murex purple dyestuff in the form of pigment with a calcium carbonate base and its application in painting was first identified and fully characterized in the context of the Xeste 3 wall paintings at Akrotiri on Thera [22–24], referring in fact to Pliny's vat-dyeing recipe for *purpurissum*.

Over the past 30 years, deep insights have been given into the production of murex purple, its coloring and medicinal properties, and the technology of its application, as a result of research findings in various disciplines [17,25–30]. The recent literature on the investigation of the chemical composition of purple, either dye or pigment, identified in archeological contexts, as well as on the factors that may affect and differentiate the color at all stages of production and the dyeing process, is extensive and yet far from being exhaustive [31,32].

This paper comparatively examines the results of the analysis of samples from three archaeological finds of the purple pigment in lump form, coming from the excavations of Akrotiri on Thera and Trianda on Rhodes, as well as of a representative sample from a purple paint detail on a wall painting at the recently excavated (2009–2012) Raos site, Thera, in which the valuable pigment was used. The chemical composition of the purple pigments and paints dating from the early Late Bronze Age (~17th century BC or earlier), identified at the three contemporary Aegean sites (Akrotiri and Raos on Thera, and Trianda on Rhodes), is discussed with reference to the archaeological context of the unique finds. Among the finds discussed, we included the lump of purple pigment found in Akrotiri, Complex D, room 12 (AKR-10891), which was the starting point and the motivation for the development of a comprehensive methodology that allows us today not only to recognize the nature the organic colorant but also to determine its exact composition in chromophores, as well as to identify the inorganic material base that makes it a pigment for painting on different substrates. Therefore, the methodology that has been progressively developed over the last 20 years and applied case-by-case to finds that came to light at different times is applied here in order to discuss the results for a set of samples that makes sense to study comparatively. New spectroscopic results, through microRaman and FTIR techniques applied on the investigated purple pigments and a purple wall painting detail, follow through previous data obtained on other true purple samples [23,24]. The spectroscopic data are combined with previously reported chromatographic studies of samples taken from the same archaeological finds to achieve their complete characterization [30]. The data collected with high performance liquid chromatography coupled with a diode array detector (HPLC–DAD) are presented here in detail and are interpreted, along with the spectroscopic results, with a fresh view from an interdisciplinary angle on the basis of new findings, allowing better understanding and interpretation of the results relating to their different excavation context as they come from different proper archaeological sites, which are, however, contemporary and belong to the same geopolitical context of the Late Bronze Age I in the Aegean.
