Tag Archives: Raw material

Introducing the International Framework project

Dieter Quast and Alexandra Hilgner from the Römisch-Germanisches Zentralmuseum (RGZM) in Mainz explain the initial questions of the project “Weltweites Zellwerk – International Framework” regarding the origin and development of garnet cloisonné jewellery in the early middle ages. Garnet gemstones from India arrived in a vast amount during the 6th century in the Merovingian kingdom in central Europe. In the 7th century, the cloisonné jewellery style was suddenly disappearing. Was it because of a change in fashion or did something happen to the former trade routes? The International Framework project, organised by the RGZM, the SAI Heidelberg and the LVR-LandesMuseum, Bonn with partners in Sweden, the UK and Hungary tries not only to find answers to these questions regarding the value and the meaning of the gemstone garnet, but also to understand the international trade and economic interactions in the “dark ages”.

Gemstones and Gem Deposits of Sri Lanka – with special emphasis on Geology, Occurrence , Varieties and Mining.

Dr. Gamini Zoysa, Ceylon Gemmological Services

Sri Lanka has long been known as one of the world’s most important gem producing countries. Specially as a leading source for fine quality Blue Sapphires & its other varieties. The genesis of gemstones in Sri Lanka has been a subject for much discussion. The gems are mostly mined from the alluvial deposits underlain by Precambrian metamorphic rocks. The main gem bearing areas are confined to the geological division called highland complex which is located in the central part of the country. Over 3200 legal gem mines have been in active operation in the past years. The depth of the gem gravel in a shaft may vary from 10 to 25 meters. There are also evidences for occurrence of primary deposits of Sapphire, Moonstone , Aquamarine, Garnet within the island. In addition to the major commercially viable gem varieties such as Sapphires, Garnet, Chrysoberyl, Topaz, Zircon, Moonstone, Tourmaline, Beryl, Quartz there are over 80 varieties of nontraditional gems are recorded.

Dienstag, den 25. Oktober, 18.15 Uhr

Römisch-Germanisches Zentralmuseum – Vortragssaal

Im Rahmen der Vortragsreihe “Weltweites Zellwerk”

See the full program here!

 

Foto: (c) http://www.aigsthailand.com

Examination of garnets and their provenance

Deutsche Version

Within my master thesis in the degree course geosciences at the Johannes Gutenberg-University in Mainz I examine the spectroscopic properties of garnets as well as the inclusions in them with different methods. The goal is to get better statements for the provenance of gemstones.

Ullmann_mikroskop
Working at the spectrometer Nicolete 6700 FT-IR to collect spectra in the mid-IR and near-IR spectral ranges.

The term Garnet stands for a group of various minerals, which are seen similarly in the crystal structure and formula. They may be partial mixable among themselves. In this case miscibility means that two or more different minerals from the group of garnets can occur together and form one unit, thus one crystal, because of their similar structural and chemical composition.
Essentially, there are two series, the Pyralspit- and Ugrandit series. The former is aluminum garnets with magnesium (Pyrope), iron [three] (almandine) or manganese (Spessartin), temptation are calcium-grenade with chromium (Uwarowit), aluminum (Grossular) or iron [two] (Andradit). The garnet deposits of the jewels in usual belong to the Pyralspit group.


Through to the large mass of processed garnet in the early European Middle Ages, provides the question for the originated area of the raw material. In addition, the garnets were cut into thin platelets and these were used across the board, but remains of garnet grinding services are not to be found yet. This raises further questions as to whether the garnets were imported already honed and in which direction they were exported as raw material as well as already honed exemplar.

Proben_Schweden_Crop
Examples of garnet platelets from a find in sweden. Foto: Michael Rychlicki

In order to determine possible areas of origin, the chemical compositions of as many garnet platelets are determined by X-ray fluorescence analysis. By this method, groups of garnets indicate which originated most likely in India, Sri Lanka and Bohemia. However, these allocations are based on the comparison with measurement results of garnets, which origin is not 100% guaranteed, because of the lack of exact details like the accurate provenance for example.

CaO/MgO-plot for the garnet finds in Sweden and in India. (In accordance to Greiff 2010)

Therefore it is the more gratifying that now samples are available that guaranteed are hailed from different federal states of India and were picked up by Borayin Larios himself.

Garnet samples from different mines in India (on 5mm square papaer)

These are examined on their chemical composition as usual and the results are compared with already collected data to improve the currently used method to assign the garnets origin by their chemistry. In addition, these samples, and other samples found in Sweden, using modern spectroscopic methods (UV-Vis, NIR-MIR and Raman spectroscopy) are examined to determine a dependence of the spectra-differences to the origin of the samples. In this manner discovered unique features may be useful as an additional discrimination criterion. Furthermore, inclusions are studied to show possible dependencies between the provenance and the other minerals.

Untersuchung von Granaten und deren Herkunft

Im Rahmen meiner Masterarbeit im Studiengang Geowissenschaften an der Johannes Gutenberg‑Universität in Mainz untersuche ich Granate mit Hilfe verschiedener Messmethoden auf ihre spektroskopischen Eigenschaften sowie ihre Einschlüsse. Das Ziel ist es, genauere Aussagen über die Herkunft der Edelsteine treffen zu können.

Ullmann_mikroskop
Arbeit am Spektrometer Nicolete 6700 FT-IR um Messungen innerhalb mittlerer und naher Infrarotstrahlung vornehmen zu können.

Der Begriff Granat bezeichnet eine Gruppe von verschiedenen Mineralen, die sich in der Kristallstruktur und -formel ähnlich sehen und untereinander teilweiße gut mischbar sein können. Unter Mischbarkeit versteht man hierbei die Tatsache, dass zwei oder mehr verschiedene Minerale der Granatgruppe aufgrund ihrer strukturellen und chemischen Ähnlichkeit gemeinsam auftreten und eine Einheit, also einen Kristall, bilden.
Im Wesentlichen gibt es zwei Reihen, die Pyralspit- und die Ugrandit-Reihe. Bei ersteren handelt es sich um Aluminium-Granate mit Magnesium (Pyrope), Eisen [dreiwertig](Almandin) oder Mangan (Spessartin), zweitere sind Kalzium-Granate mit Chrom (Uwarowit), Aluminium (Grossular) oder Eisen [zweiwertig](Andradit). Die Granateinlagen der Schmuckstücke gehören in der Regel der Pyralspit-Gruppe an.

Granatstruktur_aus_Novak_Gibbs_beschriftet_DE
Durch die große Masse an verarbeitetem Granat aus dem frühen europäischen Mittelalter stellt sich die Frage, aus welchem Abbaugebiet das Rohmaterial ursprünglich stammt. Zudem wurden die Granate zu dünnen Plättchen geschliffen und diese flächendeckend verwendet, Überreste von Granatschleifereien sind aber nicht zu finden. Wurden die Granate bereits geschliffen importiert? In welche Richtungen fand der Export des Rohmaterials, sowie der bereits bearbeiteten Steine statt?

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Beispiele von Granat-Plättchen von Funden aus Schweden. Foto: Michael Rychlicki

Um mögliche Herkunftsgebiete bestimmen zu können, werden mittels Röntgen-Fluoreszenz-Analyse die chemischen Zusammensetzungen von möglichst vielen Granat-Plättchen bestimmt. Durch dieses Verfahren lassen sich Gruppen von Granaten erkennen, welche ihren Ursprung höchstwahrscheinlich in Indien, Sri Lanka und Böhmen haben. Allerdings basieren diese Zuordnungen auf dem Vergleich zu Messergebnissen von Granaten, deren Herkunft nicht zu 100% gesichert ist, da oft exakte Details wie z.B. die genaue Fundstelle fehlen.

CaO/MgO-plot der gRanatfunde in Schweden und Indien. (In Anlehnung an Greiff 2010)

Daher ist es umso erfreulicher, dass nun Proben zur Verfügung stehen, welche garantiert aus verschiedenen Bundesstaaten Indiens stammen und von Borayin Larios selbst gesammelt wurden.

Granatproben aus Indien (auf 5mm kariertem Papier)

Diese werden wie üblich auf ihre chemische Zusammensetzung untersucht und die Ergebnisse werden mit bereits erfassten Daten verglichen um die aktuell genutzte Methode, Granaten anhand ihrer Chemie eine Herkunft zuzuordnen, verbessern zu können. Außerdem werden diese Proben, sowie weitere in Schweden gefundene Proben, mit modernen spektroskopischen Methoden (UV-Vis-, NIR-MIR- und Raman-Spektroskopie) untersucht, um eine Abhängigkeit der Spektren –Unterschiede zu der Herkunft der Probe festzustellen .Auf diese Weise entdeckte eindeutige Merkmale können als weiteres Unterscheidungs-Kriterium hilfreich sein. Ebenso werden die Proben auf Einschlüsse untersucht um eventuelle Abhängigkeiten zwischen der Herkunft und den fremden Mineralen aufzuweisen.
Diese werden wie üblich auf ihre chemische Zusammensetzung untersucht und die Ergebnisse werden mit bereits erfassten Daten verglichen um die aktuell genutzte Methode, Granaten anhand ihrer Chemie eine Herkunft zuzuordnen, verbessern zu können. Außerdem werden diese Proben, sowie weitere in Schweden gefundene Proben, mit modernen spektroskopischen Methoden (UV-Vis-, NIR-MIR- und Raman-Spektroskopie) untersucht, um eine Abhängigkeit der Spektren –Unterschiede zu der Herkunft der Probe festzustellen .Auf diese Weise entdeckte eindeutige Merkmale können als weiteres Unterscheidungs-Kriterium hilfreich sein. Ebenso werden die Proben auf Einschlüsse untersucht um eventuelle Abhängigkeiten zwischen der Herkunft und den fremden Mineralen aufzuweisen.

 

Literatur:

Novak, G. A. / Gibbs, G. V. (1971): The crystal chemistry of the silicate garnets, in: The American Mineralogist, vol. 56, 1971; 791-825.

Greiff, S. (2010): Zur Herkunft der roten Granate an Schmuckobjekten des Erfurter Schatzfundes, in: Ostritz, S. (Hrsg.). Die Mittelalterliche jüdische Kultur in Erfurt, Band 2, Der Schatzfund, Analysen – Herstellungstechniken – Rekonstruktionen; Weimar; 482-487.

An early medieval garnet workshop in Gamla Uppsala, Sweden

Lecture held by John Ljungkvist, Uppsala

 

The project “Gamla Uppsala – the emergence of a mythical centre”, has since 2009 conducted systematic studies in Gamla Uppsala to increase the knowledge of the long term structural history of the site. In the period c. 550-700, the place is transforming remarkably into a monumental site. This transformation of an already densely settled site involves the famous mounds, houses on artificial plateaus and recently discovered post row monuments. Three areas were in 2011 investigated in the centre of the Early Medieval manor area. Beyond a major reinterpretations of the great 7th c. hall/-sal, the excavation also contributed in shedding new light on settlement continuity, crafts, large scale household economy and regulations of the site between c. 400-1600 AD. Of particular interest for this presentation is the Northern Plateau, placed in a 90 degree angle in relation the great hall. This partially artificial plateau, house, in between earlier and later phases, two 6th c., two large burnt down houses from the 7th to 8th c. The older building, of which only small remains have been examined, proved to be a multi-functional crafts building where the garnet production is the most prominent activity. The building most likely houses tens of thousands of garnet fragments from the jewellery production, which makes it the so far largest production site found so far in Scandinavia.

 

Lecture held during the conference “Gemstones in the first Millennium AD. Mines, Trade, Workshops and Symbolism.” October 21st, 2015 at the Roemisch-Germanisches Zentralmuseum, Mainz (Germany).

Further reading on the web:

Blog by John Ljungkvist

Garnet jewellery in early medieval sweden (presentation)

Resources according to the archaeological research at Gamla Uppsala in Swedish:

Homepage

Arkeologerna blog posts

Societas Archaeologica Upsaliensis

Upplandsmuseet Uppsala

Facebook

The red garnet industry in contemporary Rajasthan

Lecture held by Borayin Larios, Heidelberg

 

India has become increasingly difficult. Historically believed to be a key zone for the extraction or red garnet, Rajasthan has now allegedly become a second choice for the gemstone manufacturers from Jaipur. Stake-holders in the production of gemstones presumably procure the majority of garnet rough from African countries such as Tanzania, Madagascar and Zambia, and occasionally from other parts of India, mainly from the state of Orissa.  In the fall of 2014, I ventured to look for red garnet (almandine) sources in the region of Rajasthan, and what I found was a completely different story: protected by local politicians paid off by bribes by the miners, larger mine operations of all kinds of minerals go on despite being outside the law. In the case of the gemstone quality of garnet, small-scale and artisanal mining activities are being carried out in different parts of Rajasthan and it seems that this this type of informal mining might have been the rule rather than the exception also in earlier times. In this paper, I will present my findings on how the local garnet industry is still alive in Rajasthan and what challenges it brings to the researcher to follow the trail of garnet from the mine to the costumer, not only from a historical perspective, but also in contemporary India.

 

 

The Video shows  contemporary garnet mining and processing in Rajasthan, India.

Lecture held during the conference “Gemstones in the first Millennium AD. Mines, Trade, Workshops and Symbolism.” October 20th, 2015 at the Roemisch-Germanisches Zentralmuseum, Mainz (Germany).

Garnet Jewellery in Early Medieval Sweden

Deutsche Version | Team

Present-day Sweden has a large and varied garnet material from the Iron Age. Even if there are finds dating back to the Late Roman Period most objects derive from the 5th to 8th centuries. In Sweden this time period is called the Migration and Vendel Period, and it is characterised by its regional power structures, wealthy burials and far-reaching networks of contacts. Most of the garnets are part of jewellery such as brooches but also adorning high status weaponry etc. Continue reading Garnet Jewellery in Early Medieval Sweden

Scientific and Technical Analyses of Garnet Jewellery

Deutsche Version | Team

Depending on their respective geological origin, the chemical composition of garnets varies significantly. Different areas of origin of ancient garnet can thus be distinguished by scientific analyses.

Analyses into the origins of garnet from the areas on the periphery of the Merovingian Empire, planned to be carried out within the scope of this subproject, will form the basis for an understanding of chronological changes of the distribution routes and recognising possible reasons for the “garnet route in crisis”. Continue reading Scientific and Technical Analyses of Garnet Jewellery

Garnets in Byzantine texts

Deutsche Version | Team

This part of the International Framework focuses on the use and especially on the interpretation of carbuncles in the Byzantine cultural area. The focus of this study is the question of the typically Byzantine simultaneous existence of interpretations in the ancient tradition on the one hand, and in the biblically tradition on the other hand. Furthermore, it is intended to establish the significance of carbuncles (gr. Ἄνθραξ) within a “hierarchy of gems” in Byzantium. Continue reading Garnets in Byzantine texts

Garnet on the North-western Periphery of the Merovingian Empire during the 7th Century

Deutsche Version | Team

The objective of this subproject is the archaeological and scientific analysis of garnet objects from England, Scotland and Scandinavia. The question is, why objects decorated with garnet went out of fashion on the Continent during the last third of the 6th century, while the style experienced a notable floruit in 7th-century England and Scandinavia. Continue reading Garnet on the North-western Periphery of the Merovingian Empire during the 7th Century

Towards an Understanding of Anglo-Saxon Stone Names

Deutsche Version | Team

Garnets are ubiquitous in the material culture of Anglo-Saxon England. They appear on buckles, brooches, shoulder clasps, and sieve spoons. They once lined the wings of a dragon on what is possibly the most famous Anglo-Saxon artefact, the helmet from the Sutton Hoo ship burial. Their beauty was, perhaps, imitated in ink and vellum in images which sought to recreate the beauty of jewels on manuscript. Continue reading Towards an Understanding of Anglo-Saxon Stone Names

Garnet in South Asia

Historical and Archaeological Sources

Deutsche Version | Team

The Indological sub-project of the International Framework will concentrate on two thematic foci. The first is the study and translation of textual sources describing pre-modern knowledge about gemstones and their specific effects. Here we deal with diverse texts composed in Sanskrit which not only present various characteristics of gemstones and their astrological, medical and spiritual potency, but which also relay the legends and myths associated with them. Continue reading Garnet in South Asia