SYNTHESIS AND ACID RESISTANCE OF MAYA BLUE PIGMENT*

Maya blue is an organo‐clay artificial pigment composed of indigo and palygorskite. It was invented and frequently used in Mesoamerica in ancient times (eighth to 16th centuries). We analyse in this paper one of the characteristics of Maya blue that has attracted the attention of scientists since its rediscovery in 1931: its high stability against chemical aggression (acids, alkalis, solvents, etc.) and biodegradation, which has permitted the survival of many works of art for centuries in hostile environments, such as the tropical forest. We have reproduced the different methods proposed to produce a synthetic pigment with the characteristics of the ancient Maya blue. The stability of the pigments produced using either palygorskite or sepiolite has been analysed by performing acid attacks of different intensities. The results are analysed in terms of pigment decolouration and destruction of the clay lattice, revealed by X‐ray diffraction. Palygorskite pigments are much more resistant than sepiolite pigments. It is shown that indigo does not protect the clay lattice against acid aggression. We show that Maya blue is an extremely resistant pigment, but it can be destroyed using very intense acid treatment under reflux.     

On The Grounds Of Post‐Byzantine Greek Icons

The grounds of 51 post‐Byzantine icons (Eastern Orthodox panel paintings) were studied by means of analytical techniques. The artefacts cover the period from the mid‐15th to the mid‐19th century and originate mainly from western (Epirus and the Ionian Islands) and southern Greece (Crete). The findings are examined in the light of technical recipes from related areas and eras, while special insights are gained from the exploration of a gypsum processing recipe by Dionysius of Fourna. A spectrum of ground fabrication practices that is richer than that reported so far or can be deduced from surviving Greek recipes is documented; three instances of ‘grosso‐sottile’ type grounds and a case of ‘inverse grosso‐sottile’ ground are among the reported novel, for post‐Byzantine icons, findings. Moreover, a case of an early icon restoration intervention is documented.     

Charcoal analysis of industrial fuelwood from medieval and early modern iron-working sites in Bilsdale and Rievaulx,North Yorkshire,UK: evidence for species selection and woodland management

Abstract

This paper presents the results of species diversity and dendrological analyses of archaeological charcoal excavated from medieval and early modern iron production sites in Bilsdale, and at Rievaulx in the neighbouring valley of Ryedale, North Yorkshire, UK. Standard methods of quantification are used to assess species diversity, sampling sufficiency and taxa presence. The assessment of dendrological features provides additional evidence for growth trends and cutting cycles analogous with cyclical woodland management, as well as environmental and growing conditions. Analysis of archaeological charcoal from four medieval bloomery furnace sites in Bilsdale, and from the site of the hammersmithy and blast furnace at the early modern iron works at Rievaulx, provide comparable data-sets which indicate a change in cutting practise and dominant species selection for industrial fuelwood occurred between the 12th- and mid-16th centuries AD. Results show that dominant species presence changed from an admixture of predominantly birch (Betula sp.) and hazel (Corylus avellana) sourced from small calibre branchwood and stemwood used in the medieval bloomery furnaces, to a dominant oak (Quercus sp.) presence from standard sources used at the Rievaulx iron works by the mid-16th century. Whilst it is uncertain whether this change in dominant species composition and the source of industrial fuelwood is related to changes in local availability, or the result of the technological transition to blast furnace processing which occurred at this time, estate records reveal a woodland management campaign was instigated to supply and maintain fuelwood supplies to the iron works at Rievaulx which coincides with the introduction of Tudor arboricultural legislation in the 1540s.     

Two Byzantine Albanian icons: a non-destructive archaeometric study

The present work is part of a project aimed at studying the pigments and painting techniques used by Albanian iconographers to produce Byzantine and post-Byzantine icons dating from the fourteenth to the nineteenth centuries; the state of conservation of these icons was also explored. Inorganic pigments are identified by means of X-ray fluorescence, reflectance spectrophotometry and UV fluorescence analysis. These analysis techniques were performed to discriminate between pigments on the basis of their typical features. Moreover, the study of the optical properties of paintings is of fundamental importance for correct restoration. This work enabled us to recognise the palette used in two artworks by anonymous painters of the fourteenth and fifteenth centuries. Only three small samples were taken from the edge and the back of the wooden tables in order to achieve information on preparatory layers. Twelve to fourteen non-destructive measurements were made to characterise the palette used by the two anonymous painters.     

Examination of some pigments,grounds and media from Egyptian cartonnage fragments in the Petrie Museum,University College London

A number of cartonnage fragments from the collections of the Petrie Museum, UCL, were examined to identify pigments, media and grounds. The different types of cartonnage made in ancient Egypt are reviewed. Special attention was paid to green pigments, which were shown to be of green earth, or a mixture of Egyptian blue and a yellow, usually goethite or orpiment. Green earth was found in one artefact, dated to the 9th century BC: all other examples were from the Graeco-Roman period. No copper-organometallic greens were present in the examples studied, or Egyptian green, or malachite. Binding media was identified both by ELISA and by GC/MS. A pink colourant was identified as madder, while lead white was used as a white in one example, showing the influence of Roman and Greek pigments on Egyptian art in these later periods. Plant gum, egg, and animal glue were found in different fragments, with mixed media in a few cases. Moganite was found associated with quartz in some preparatory layers by X-ray diffraction, which has not been reported previously as a constituent of ground layers in Egyptian artefacts.     

PIGMENT IDENTIFICATION IN GREEK POTTERY BY RAMAN MICROSPECTROSCOPY*

Raman microspectroscopy (RMS) is now established as a key technique for the identification of pigments of archaeological pottery that permits the in situ study of art objects by a non‐destructive procedure. The information obtained represents a great aid to restoration and conservation techniques. In this work, the chemical nature of the red, black and white pigments of five samples of Greek pottery from the end of the fifth century and the first half of the fourth century bc , exhumed from the Iberian necropolis of Cabezo Lucero (Guardamar del Segura, Alicante, Spain), has been identified. The black and the red pigments are found to be magnetite (Fe₃O₄) and hematite (α‐Fe₂O₃), respectively. The white pigment is found, for the first time, to be composed of alumina (α‐Al₂O₃ and γ‐Al₂O₃) probably yielded by the thermal decomposition of Greek bauxite.     

DOMUS AUREA,THE ‘SALA DELLE MASCHERE’: CHEMICAL AND SPECTROSCOPIC INVESTIGATIONS ON THE FRESCO PAINTINGS

In this paper, data collected from the wall fresco paintings of room 114, called the ‘Sala delle maschere’, of the Domus Aurea in Rome is analysed. The chemical composition of the efflorescence is investigated by infrared spectroscopy. The colour palette is determined by means of EDXRF, Raman spectroscopy and visible reflectance spectroscopy. EDXRF has allowed an extensive mapping of the elements present in the pigments and plaster; whilst in‐situ Raman spectroscopy has been determinant for attributing the molecular composition of the pigments in a number of doubtful cases. Most pigments identified are typical of Imperial Roman fresco paintings (first to fourth centuries AD) ( Ward‐Perkins 1981 ); more interestingly, we found evidence of fragments painted with Egyptian blue, which was normally used mostly in official rooms.     

Smalt production in the Ore Mountains: Characterization of samples related to the production of blue pigment in Bohemia

The study deals with the chemical composition of samples related to the production of a blue pigment/smalt. The samples examined come from the regions of Soví huť and Horní Blatná (north-west Bohemia) dating to the 16th and 17th centuries. These locations are often mentioned in relation to the discoverer of smalt production technology: Christopher Schürer. The aim of the study is to evaluate the chemical composition of samples from both localities as well as with respect to the ores occurring in the given regions. The samples can be divided into two basic groups. The first clearly represents smalt (potassium glass coloured with cobalt), while the second apparently constitutes the samples of the so-called ‘speiss’ (an aluminosilicate mass with metallic compounds). The analysis of the smalt confirmed the representation of minor elements bismuth and nickel (always) and uranium and molybdenum (rarely), which are found in Co ores from the Ore Mountains. The paper is the first to present the composition of actual blue pigment finds originating directly from the production sites, while the available literature has so far only reported the results of analyses of the pigments already used when referring to the Ore Mountains.     

Identification of organic materials in icons of the Cretan School of iconography

The Cretan School of iconography is the last great flowering of the traditional Byzantine painting manner, which is however influenced by different schools and western art. Despite their historical significance, icons of the Cretan School have been rarely studied through modern chemical techniques and therefore very few information is available on the materials used by the Cretan painters. In the present investigation, the organic materials contained in several icons of the Cretan School of Iconography from the collection of the Benaki Museum, Athens, Greece, are analyzed and identified by High Performance Liquid Chromatography coupled to a Diode Array Detector (HPLC–DAD) and Gas Chromatography with Mass Spectrometry (GC–MS).The HPLC–DAD results provide support to a recently published report which showed that kermes used in “Cretan” icons of 15th century and early 16th century was replaced by cochineal which was used in icons dated after early 16th century. This trend is known for western art and it is now proved for Cretan icons, showing thus the influence of the Cretan painters by other European painting schools. Other dyes detected in the historical samples, extracted from Cretan icons are madder (possibly Rubia tinctorum L., according to HPLC profiles) and indigoid dyes. Oils, such as linseed and walnut oil, are identified in samples extracted from the seven icons tested by GC–MS. Egg yolk is identified in the extract of only one icon and animal glue, originated most likely from the gesso ground, is found in six samples. Other organic materials detected by GC–MS were wax, as well as synthetic resins, applied during conservation treatments.     

ARCHAEOLOGICAL,STYLISTIC AND SCIENTIFIC RESEARCH ON 11TH–13TH CENTURY AD PAINTED FRAGMENTS FROM THE SAN GIOVANNI BATTISTA CHURCH IN CEVIO (SWITZERLAND)

The painted fragments collected during the archaeological excavation campaign in the San Giovanni Battista church in Cevio represent a unique patrimony of Romanesque wall painting in Tessin, Switzerland, having a strong stylistic linkage with the Lombardic art of the same period. The archaeological and stylistic research allowed the fragments to be dated between the 11th and 13th centuries ad and to group them in three chronological phases. The scientific research (p‐XRF, OM, SEM–EDS, FTIR and XRD) was aimed at characterizing the pigments and the pictorial techniques used. Important changes occurred in terms of some pigments used during the 11th and 12th centuries: in particular, azurite was used to decorate the earlier wall paintings while lapis lazuli was used for the 12th‐century ones. During the second period, lead‐based pigments (lead white and minium) were introduced into the palette. The use of natural yellow and red ochres and green earth was common for the three periods. The fresco technique was generally used, except for the application of azurite and lead‐based pigments, where the a secco technique was adopted. The integrated research is a contribution to the knowledge of Romanesque art in the Insubric Region.     

THE BLUE ENAMELS IN THE BAROQUE DECORATIONS OF THE CHURCHES OF PALERMO,SICILY: FE2+‐COLOURED GLASSES FROM LIME KILNS*

Deep blue glasses coloured by octahedral Fe²⁺ cations are often reported as textbook examples of blue pigmentation. However, despite the possibility of laboratory synthesis under reducing conditions, to date there are no well‐reported occurrences of their production and use in the past. A thorough historical, ethnographic, mineralogical, and chemico‐physical investigation of the ‘smaltini di calcara’ from several baroque churches in Palermo, Sicily, has revealed that the blue enamels widely used for altar decorations in the 17th and 18th centuries are actually a unique case of ancient blue glasses pigmented by divalent iron cations in distorted octahedral coordination. This mixed‐alkali glass was accidentally produced under severely reducing conditions in the local kilns during production of lime.     

IDENTIFYING THE PLANT ORIGIN OF ARTISTS' YELLOW LAKE PIGMENTS BY ELECTROSPRAY MASS SPECTROMETRY

Dyes containing flavonoids are found in yellow lake pigments used as artists' materials. Pre‐treating a sample of a flavonoid‐based lake pigment with an acidic ion exchange resin followed by reversed‐phase HPLC electrospray mass spectrometry enables the identification of key diagnostic yellow compounds, even when the pigment is bound in paint media. Reference raw plant materials of weld and buckthorn berries were also treated similarly for comparison with the lake pigments derived from these plants. This method is suitable for microsamples and thus suitable for analysis of samples that can be ethically removed from works of art in the course of their conservation. The flavonoid content is analysed and plant origins are suggested for yellow lake samples taken from Reclining Tiger by Jean‐Baptiste Oudry and the 1893 version of The Scream by Edvard Munch.     

THE ‘DELLA ROBBIA BLUE’: A CASE STUDY FOR THE USE OF COBALT PIGMENTS IN CERAMICS DURING THE ITALIAN RENAISSANCE*

The morphologies and elemental compositions of cobalt blue glazes are studied in 56 dated and undated terracotta sculptures from the Florentine della Robbia school. The data allow tracing of the pigments through correlations amongst elements that are known to be constituents of the cobalt minerals. The supply of such minerals from the Erzgebirge region in Renaissance times is compatible with our data. A substantial change in the materials is marked by the presence of arsenic and bismuth in the glaze, and by reduced amounts of iron and nickel just before 1520. We speculate that this is due to procedures introduced to industrialize the production of the blue pigment. The exploitation of different cobalt minerals in association with different production procedures may explain the variability of compositions that we observe in this unique ensemble.     

THE CHEMICAL COMPOSITION OF BLUE PIGMENT ON CHINESE BLUE‐AND‐WHITE PORCELAIN OF THE YUAN AND MING DYNASTIES (ad 1271–1644)*

The chemical compositions of the glazes and pigments of 39 blue‐and‐white porcelains of Ming Dynasty date and three of Yuan date were examined by SR‐XRF. Both the analysis of the Fe/Mn ratio in the light blue areas of the glaze and a comparison of the Fe/Mn values between light blue, dark blue and clear glaze areas reveals that the samples can be divided into three groups. The results indicate that there are two significant changes of provenance of blue pigment during the Ming Dynasty and that some kinds of pigment were most probably imported from the Middle East. Considering literature records and other scholars’ studies, an outline picture of the pigment used on Chinese blue‐and‐white porcelain produced in Jingdezhen in the Yuan and Ming Dynasties is presented.     

ANTIMONATE OPAQUE GLAZE COLOURS FROM THE FAIENCE MANUFACTURE OF LE BOIS D’ÉPENSE (19TH CENTURY,NORTHEASTERN FRANCE)*

Three types of antimony‐based, opaque ceramic colours were used in the faience workshop of Le Bois d’Épense during the first decades of the 19th century; that is, yellow, tawny and green. Yellow is generated by lead antimonate crystals (Naples Yellow), which are incorporated into an uncoloured glass matrix. According to SEM–EDS measurements, these pigments contain iron. The tawny colour is the optical result of the combined presence of similar yellow, iron‐bearing lead antimonate particles in a Fe‐rich, brownish glass matrix. The green opaque colour is produced by the combination of a blue cobalt glass and yellow Pb–Sn–Fe‐antimonate crystals. Cores of zoned pigments lighten the recipes, according to which the pigments were produced. First, they were synthesized by calcination, ground and then mixed with a colourless, brown or blue glass powder. The resulting powder mixture was added to a liquid agent and used as high‐temperature ceramic colour.     

Physicochemical characterization and provenance of colouring materials from Akrotiri-Thera in relation to their archaeological context and application

An assemblage of approximately 500 colouring materials and objects related to their use, found in different contexts and forms at Akrotiri, Thera, was recently investigated. The items date to the Early, Middle and Late Cycladic Bronze Age (c. 3000?C1600 bc) and include materials or pigments found in their natural state, in specifically made forms or inside vessels. Some of the contexts do not provide any indication of the pigments?? use, storage, trade or application. Among the investigated materials, which include red and yellow ochres and blue riebeckite, are those that can be associated with pigments that were widely used in the past in wall paintings or to decorate pottery. There is also evidence for the selective use of purple pigments, which were derived from shellfish, in wall paintings. However, there are other raw colouring materials, such as lead pigments that have not been previously known to have been used in wall paintings or in any other applications during the prehistoric period in the Aegean. A thorough macro- and microscopic visual examination of the quality and morphology of these items enabled the identification of physical features (colour, homogeneity, grain size and shape) that indicate their nature or degree of processing. To identify the mineral composition of the pigments and to investigate their provenance from a geological perspective, quantitative X-ray diffraction (XRD) analysis was conducted. For those samples requiring additional information on their composition and for the refining or confirming of the XRD data, scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM-EDX), micro-Raman and Fourier transform infrared (FT-IR) spectroscopies were performed. This work is part of a larger project, supported by Institute for Aegean Prehistory, that aims to clarify major archaeological queries that are not restricted to the identification of the nature, composition and provenance of the colouring materials but extend to aspects of their selection, preparation and application techniques used during the Early to the Late Bronze Age.     

Multi-analytical techniques for the study of pre-Columbian mummies and related funerary materials

Due to a paucity of original written information, we base our knowledge of the pre-Columbian civilizations of Latin America on archaeological and archaeometric analysis. Particularly, the analytical study of funerary materials collected by conquerors in historical times and archaeologists nowadays during their travels and expeditions contributes to a better understanding of religious practices and social organisation. In the present study, a multi-analytical approach is presented which was used for the characterisation of red and blue organic dyes, inorganic pigments and embalming materials in various archaeological finds from the necropolis of Ancòn (Peru). These included the funerary clothes belonging to a set of three mummies, dated between the 11th and the 13th century AD. Chromatographic and spectrometric techniques were used: high performance liquid chromatography with UV-Visible detector (HPLC-UV-Vis) for identifying organic dyes, scanning electron microscopy with energy dispersive X-ray spectrometer (SEM-EDX) for recognising pigments, and gas chromatography with mass spectrometric detection (GC/MS) for analysing organic embalming materials. This multi-analytical approach enabled us to characterise a range of materials. The presence of red anthraquinoid dyes and blue indigoid ones was assessed, although it was not always possible to identify the original source with certainty. Cinnabar was identified as the colouring material applied to one mummy's hair. The molecular markers of conifer resin were detected in the bandages. The analytical results highlighted the use of a number of hitherto unknown dyes and embalming materials in Peruvian funerary rituals.     

The production technology of Egyptian blue and green frits from second millennium BC Egypt and Mesopotamia

The microstructures and chemical compositions of some 55 Egyptian blue and green frit samples from New Kingdom Egypt and 15th century BC Mesopotamia are determined using analytical scanning electron microscopy, the main focus being on frit cakes, powder residues, and frit vessel and bead fragments from one of the “factory areas” at Amarna in Middle Egypt. Replicate Egyptian blue frits produced in the laboratory are similarly investigated. Comparison of the microstructures of the ancient and replicate samples suggest that frit cakes are the primary product, and that these were ground to produce the powder, and then moulded to shape and refired to produce the vessels and beads. Egyptian blue and green frits are shown to be distinct pigments, the pigment produced depending on the relative proportions of copper oxide and lime in the mixtures. The bulk and glass phase compositions are used to try to infer the different sources of the quartz, lime, copper and alkali flux used in the production of frits from Egypt and Mesopotamia. An estimate is made of the scale of production of Egyptian blue frit in New Kingdom Egypt.     

ANALYSIS OF ROMAN WALL PAINTINGS FROM THE THERMAE OF ‘IULIA CONCORDIA’

Twenty‐six wall painting fragments and some plaster, ‘intonachino’ and stucco samples, discovered at Iulia Concordia, have been studied by different analytical techniques to gain information about the pigment nature and the composition of the materials. The presence of calcite, dolomite and aragonite allow the distinction of four groups of wall samples varying in the nature of pigments and in the application technique. These differences can be attributed to different execution times or, more probably, to the arrangement of the rooms in the building structure. The nature of the pigments found in the Thermae of Iulia Concordia appears similar to that found in other Roman villas of Venetia et Histria, with the use of precious pigments such as Egyptian blue and cinnabar.