An improved HPLC method coupled to PCA for the identification of Tyrian purple in archaeological and historical samples

More than just a color: Archaeological, analytical, and procedural aspects of Late Bronze Age purple-dye production at Cape Kolonna, Aegina

Excavations in the Eastern Suburb of Bronze Age Aegina Kolonna revealed the destruction deposit of two sequenced Early Mycenaean buildings (phase Late Helladic IIA; 16th century BC). The older building is interpreted as a widely undisturbed production site of purple-dye based on indicative finds such as ceramic sherds containing analyzable quantities of pigment, high amounts of mollusk shells, and a few functional facilities. Chemical analysis by HPLC and malacological determination revealed that the banded dye-murex (Hexaplex trunculus) was used almost exclusively. The presence of crushing tools and a waste disposal pit provide insight into the technical process of dye production. Additionally, skeletal remains of heavily burnt infantile and juvenile piglets, kids, or lambs were found in the purple workshop area. The evidence may be better explained by ritual activities aimed at promoting the highly meaningful event of purple production, rather than by normal food consumption practices.

Identification of Dyes in Coptic Textiles from the Museum of Faculty of Archaeology, Cairo University

High Performance Liquid Chromatography coupled to a Diode-Array-Detector (HPLC-DAD) is used to investigate samples which were extracted from ancient Egyptian textiles (4th–5th c. AD) of the Museum of Faculty of Archaeology, Cairo University. Madder is identified in several samples. According to semi-quantitative results, which are obtained from HPLC peak areas measured at 254 nm, madder that is rich in purpurin and poor in alizarin is identified in samples which were treated (i) only with madder and (ii) with madder and either indigo/woad (Indigofera species and other/Isatis tinctoria L.) or weld (Reseda luteola L.). The madder dye used in these samples could have been originated from Rubia peregrina L. However, the possible use of Rubia tinctorum L. (or other plants of the Rubiaceae family) by the Egyptian dyers cannot be ruled out, particularly if methods were developed by the ancient dyers to affect and control the relative composition of madder dye. The HPLC peak area ratio of alizarin versus purpurin is very high (>2.2) for samples which were treated with madder (probably originated from R. tinctorum) and a tannin source. Finally, in some samples, only indigoid dyes (indigo/woad) are identified.

Early evidence of royal purple dyed textile from Timna Valley (Israel)

In the context of a broad study aimed at examining dyeing technologies in the Timna textiles collection, three samples of prestigious fibers dyed with murex sea snail were identified. Our identification is based on the presence of 6-monobromoindigotin and 6,6-dibromoindigotin components (detected using HPLC analysis), which is considered unequivocal evidence for the use of murex-derived purple dyestuff. Furthermore, by comparing the analytical results with those obtained in a series of controlled dyeing experiments we were able to shed more light on the specific species used in the dyeing process and glean insights into the ancient dyeing technology. The samples originated from excavations at the extensive Iron Age copper smelting site of “Slaves’ Hill” (Site 34), which is tightly dated by radiocarbon to the late 11^th–early 10^th centuries BCE. While evidence for the important role of purple dyes in the ancient Mediterranean goes back to the Middle Bronze Age (early 2^nd millennium BCE), finds of dyed textiles are extremely rare, and those from Timna are the oldest currently known in the Southern Levant. In conjunction with other observations of the very high quality of the Timna textiles, this provides an exceptional opportunity to address questions related to social stratification and organization of the nomadic society operating the mines (early Edom), the “fashion” of elite in the region during the early Iron Age, trade connections, technological capabilities, and more.

Review and New Evidence on the Molluscan Purple Pigment Used in the Early Late Bronze Age Aegean Wall Paintings

The production and use of the pigment extracted from the murex molluscs is discussed here in association with the purple textile dyeing industry in the Prehistoric Aegean. “True” purple has been identified in a number of archaeological finds dating from the early Late Bronze Age, found in old and recent excavations at three different but contemporary sites: Akrotiri and Raos on Thera, and Trianda on Rhodes. The chemical composition of the shellfish purple pigment either found in lump form or applied on wall paintings is discussed in relation to the archaeological context of several examined finds and with reference to Pliny’s purpurissum. The results of a comprehensive methodology combining new data obtained with molecular spectroscopies (microRaman and FTIR) and already reported data obtained with high performance liquid chromatography coupled with a diode array detector (HPLC–DAD) applied to samples of the murex purple finds are discussed in comparison to published data relating to few other instances of analytically proven murex purple pigment found in the Aegean over the timespan of its documented exploitation.

Analysis of Natural Dyes from Historical Objects by High Performance Liquid Chromatography and Electromigration Techniques

Based on material published between 1989 and 2018 in this paper high performance liquid chromatography and electromigration techniques used in studies of natural dyes that can be found in historical objects are rewieved. Different aspects of analysis have been discussed: the stationary and mobile phase, the choice of sample solvent, methods of extraction and detection, including sensitivity parameters, such as LOD and/or LOQ. The discussed dyes have been divided into three categories (a) red antraquinone dyes along with dyes extracted from bark and tree juices, (b) yellow flavonoid dyes and saffron and (c) blue indigoid dyes. The main markers (chromophores or auxochromes) typical for each dye source were presented which allows to identify specific species of source plants and animals. The first part of the study involved the analysis of most critical findings when it comes to HPLC or represented an significant analytical approach. The second part of the study is focused on different aspects of electromigration techniques application in analysis of natural dyes with special attention paid on such parameters as the running buffer/mobile phase composition and sample solvent. Detection methods along with LOD and LOQ comparison in HPLC and electromigration techniques were also discussed. Methods of sample preparation, such as hydrolysis and extraction, used in HPLC and electromigration techniques were also briefly discussed.

Dyes from the Ashes: Discovering and Characterizing Natural Dyes from Mineralized Textiles

Vesuvius eruption that destroyed Pompeii in AD 79 represents one of the most important events in history. The cataclysm left behind an abundance of archeological evidence representing a fundamental source of the knowledge we have about ancient Roman material culture and technology. A great number of textiles have been preserved, rarely maintaining traces of their original color, since they are mainly in the mineralized and carbonized state. However, one outstanding textile sample displays a brilliant purple color and traces of gold strips. Since the purple was one of the most exclusive dyes in antiquity, its presence in an important commercial site like Pompeii induces us to deepen the knowledge of such artifacts and provide further information on their history. For this reason, the characterization of the purple color was the main scope of this research, and to deepen the knowledge of such artifacts, the SERS (Surface Enhanced Raman Scattering) in solution approach was applied. Then, these data were enriched by HPLC-HRMS analyses, which confirmed SERS-based hypotheses and also allowed to hypothesize the species of the origin mollusk. In this context, a step-by-step integrated approach resulted fundamental to maximize the information content and to provide new data on textile manufacturing and trade in antiquity.

A Review on the Archaeological Chemistry of Shellfish Purple

Shellfish purple, also known as Tyrian purple and royal purple, has a long history, which has been revealed and documented in recent years through valid physicochemical studies using sophisticated techniques. The aim of the work was to summarize the conclusions of these studies and to describe the results of two unpublished investigations regarding the (i) identification of shellfish purple in a textile (4th century BCE) from ancient Macedonia and (ii) dramatic effect of the dyeing conditions on the composition of the purple dye. Moreover, a critical discussion is included about the discovery of the shellfish pigment and dye based on the available scientific evidence. Previously published reports describing the identification of the shellfish colorant in objects of the cultural heritage were carefully summarized. Shellfish purple was not used only as colorant, but it served other purposes as emphasized in this review. In particular, examples for the use of shellfish purple in medicine, grave goods and fillers and plasters in walls, were described. Examples of materials and methods that were used in the past to produce “fake” purple, imitating the aesthetic result of the valuable royal marine material were summarized. Finally, the solubility of indigoids was discussed using modern approaches of physical chemistry.

Volatile and bioactive compounds in opercula from Muricidae molluscs supports their use in ceremonial incense and traditional medicines

Muricidae molluscs are the source of a valuable purple dye that was traded as a luxury item in the Mediterranean region and by the late Byzantine was reserved for royalty and priests. Less well known is the use of muricid opercula in sacred incense and traditional medicines, although they are still used as rare ingredients today. This study provides the first chemical assessment of opercula from Muricidae, based on several traditional preparation procedures. Chemical analysis of opercula smoke revealed aromatic phenols, which act as fragrance stabilisers and produce a "medicinal" odour. Analysis of lipid extracts revealed pharmaceutically active compounds, including brominated indoles, choline esters and adenosine, consistent with their traditional medical applications. Depending on the preparation procedures, toxic pyridine was also detected. ICP-MS analysis of muricid opercula shows the presence of essential macro and microelements, as well as metals, some of which exceed the recommended safe levels for human use. Nevertheless, these findings support the Muricidae as an historically important marine resource, providing Biblical dyes, medicines and perfume. The opercula contains biologically active compounds and produces smoke containing volatile scent compounds, consistent with their identification as the most likely source of onycha, a controversial ingredient in sacred incense.

Early evidence (late 2nd millennium BCE) of plant-based dyeing of textiles from Timna, Israel

In this article, we focus on the analysis of dyed textile fragments uncovered at an early Iron Age (11^th-10^th centuries BCE) copper smelting site during new excavations in the Timna Valley conducted by the Central Timna Valley (CTV) Project, as well as those found by the Arabah Expedition at the Hathor Temple (Site 200), dated to the Late Bronze/early Iron Ages (13^th-11^th centuries BCE). Analysis by HPLC-DAD identified two organic dyestuffs, Rubia tinctorum L. and indigotin, from a plant source (probably Isatis tinctoria L.). They are among the earliest plants known in the dyeing craft and cultivated primarily for this purpose. This study provides the earliest evidence of textiles dyed utilizing a chemical dyeing process based on an industrial dyeing plant from the Levant. Moreover, our results shed new light on the society operating the copper mines at the time, suggesting the existence of an elite that was interested in these high quality textiles and invested efforts in procuring them by long-distance trade.

Investigation of crimson-dyed fibres for a new approach on the characterization of cochineal and kermes dyes in historical textiles

The colorant behaviour of cochineal and kermes insect dyes in 141 experimentally-dyed and 28 artificially-aged samples of silk and wool was investigated using ultra-high performance liquid chromatography coupled to photodiode array detector (UHPLC-PDA), liquid chromatography electrospray ionisation mass spectrometry (LC-ESI-MS) and image scanning electron microscopy - energy dispersive X-ray spectroscopy (SEM-EDX). Partial-least squares discriminant analysis (PLS-DA) was then used to model the acquired UHPLC-PDA data and assess the possibility of discriminating cochineal insect species, as well as their correspondent dyed and aged reference fibres. The resulting models helped to characterize a set of 117 red samples from 95 historical textiles, in which UHPLC-PDA analyses have reported the presence of cochineal and kermes insect dyes. Analytical investigation of the experimentally-dyed and artificially-aged fibres has demonstrated that the ratio of compounds in the insects dye composition can change, depending on the dyeing conditions applied and the type of fibres used. Similarities were observed when comparing the UHPLC-MS and SEM-EDX results from the dyed and aged references with the historical samples. This was verified with PLS-DA models of the chromatographic data, facilitating the classification of the cochineal species present in the historical samples. The majority of these samples were identified to contain American cochineal, which is in agreement with historical and dye identification literature that describe the impact of this dyestuff into European and Asian dyeing practices, after the Iberian Expansion in the 16th century. The analytical results emphasize the importance of using statistical data interpretation for the discrimination of cochineal dyes, besides qualitative and quantitative evaluation of chromatograms. Hence, the combination of UHPLC-PDA with a statistical classification method, such as PLS-DA, has been demonstrated to be an advisable approach in future investigations to assess closely related species of natural dyes in historical textile samples. This is particularly important when aiming to achieve more accurate interpretations about the history of works of art, or the application of natural dyes in old textile production.