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Conference Proceedings: Gemstones in the first Millennium

Researchers from different fields like archaeology, history, philology and natural sciences present their studies on ancient gemstones. Using precious minerals as an example, trade flows and craftsmanship, but also utilisation and perception are discussed in a cross-cultural and diachronic approach. The present volume aims at three main questions concerning gemstones in archaeological and historical contexts: »Mines and Trade«, »Gemstone Working« as well as »The Value and the Symbolic Meaning(s) of Gemstones«.

 

This volume contains the proceedings of the conference »Gemstones in the first Millennium AD« held in autumn 2015 in Mainz, Germany, within the scope of the BMBF-funded project »Weltweites Zellwerk – International Framework«.

You can preview the table of content and a preface here.

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”.

Technical Experiments 1: Producing a piece of silver foil

As an alternative to high karat gold foils fire-gilt silver foils have been used to produce the patterned Early Medieval backing foils. For my experiments, I needed a silver foil of a material thickness of 0,025 to 0,03 mm. My starting material was a sheet the size of 10×10 cm and a thickness of 1 mm. It was composed of 93,5% silver, 6,2% copper and 0,3% zinc. The authentic way to reduce the metal thickness would have been to draw down the material by forging. but to save time I decided to thin the sheet by rolling using a hand-operated rolling mill. The metal is worked in a cold state. It is primarily stretched in length. Because the process creates stresses in the crystal structure, the workpiece has to be annealed after several passes though the rolls: You have to heat it to a red state and then cool it down. Rolling the silver sheet to a material thickness of 0,03 mm would mean that its length expands up to 4 m! So repeated cutting off of smaller pieces was necessary. I started to roll the sheet immediately, reducing the distance between the rollers step by step, and I could go on until a material thickness of 0,1 mm was reached. Then the gap between the rollers couldn’t be made any smaller. So I continued sandwiching the silver between two copper sheets. During the whole rolling process the workpiece had been periodically annealed. The thinner the sheet became the greater was the danger of melting. Finally, I held two silver sheets, sizes 2,7×6,6 cm and 2,7×5,2 cm, of a material thickness of 0,03 mm in my hands, with some small stress cracks along the edges and both a little bit warped, probably because of an irregular roller pressure.

Fig.1: surface area melted during the annealing process, image field: 10,5×15,5 mm (photo: RGZM/Stempel)
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Fig. 2: stress cracks along the edge of the sheet, image field: 8×12,6 mm (photo: RGZM/Stempel)

 

Lit.: E. Brepohl, Theory and Practice of Goldsmithing, Brunswick 2001.

Manufacturing and uses of backing foils – some technical experiments

Hello, I am Christiane Stempel, goldsmith, conservator and responsible for the technological examination of Early Medieval garnet objects that have been brought to the Römisch-Germanisches Zentralmuseum in Mainz for scientific analyses within the project “Weltweites Zellwerk”.

During my work, I made some observations that raised questions regarding the manufacturing and the use of the patterned foils behind the garnets.

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Fig. 1: Schematic figure of an Early Medieval garnet cloisonné (photo: RGZM/Ober)

Transparent stones were often underlaid with gold foils to reflect the light through the stone. This is particularly important when the stone is backed up with cement. In the Early Medieval period textured backing foils were used on a large scale. The three-dimensional pattern increased the reflective effect. I examined a great number of objects from different find-spots in Sweden, Anglo-Saxon England and the Rhineland and I found all the varieties of pattern commonly known from the literature such as standard waffle, boxed waffle (Varying in the number of enclosed squares [9 to 25]), ring-and-dot, lozenge, boxed lozenge and rectangle (stack bond). They only differ in fineness (number of lines/mm), depth of texture and contour sharpness.

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Fig. 2 a-f: Foil pattern (RGZM/Stempel)

 

Unfortunately, the project nears its end and I would like to use the remaining time to carry out some technical experiments:

Producing the pattern

There are indications (see figures 3-7) that at least a number of foils weren’t manufactured with dies. It looks as if lines were traced immediately on to the foils to form the grid pattern.

Fig. 3: Buckle, Ailenberg, Württembergisches Landesmuseum Stuttgart A.V. III333 (photo: RGZM/Stempel)
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Fig. 4: Disc brooch, Junkersdorf, Römisch-Germanisches Museum Köln 51,539 (photo: RGZM/Stempel)
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Fig. 5: Disc brooch, Monsheim, Römisch-Germanisches Zentralmuseum Mainz O.15370 (photo: RGZM/Stempel)
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Fig. 6: Disc brooch, Iversheim, LVR Landesmuseum Bonn 1960.667 (photo: RGZM/Stempel)
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Fig. 7: Disc brooch, St.Severin, Römisch-Germanisches Museum Köln 50.286 (photo: RGZM/Stempel)

N. D. Meeks and R. Holmes described in their article “The Sutton Hoo Garnet Jewellery” an experiment with a scriber that they used to draw the lines directly onto the foils. But in their opinion, the result was not satisfying. (N. D. Meeks/R. Holmes, The Sutton Hoo garnet jewellery: an examination of some gold backing foils and a study of their possible manufacturing techniques. Anglo-Saxon Studies in Archaeology and History 4, 1985, 143-157.) I would like to pick up the idea again, but instead of a scriber I will do the work with a profiled hand-operated tool, comparable to a creaser. It is used until today in bookmaking and leather processing to imprint decorative lines onto a leather surface. In contrast to a pointed scriber the elongated working face of a creaser can be of any cross-section.

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Fig. 8: Creaser (photo: RGZM/Steidl)

 

The theory that has to be verified in practice is as follows:  The grid pattern can be formed with a sliding forward motion of the tool, running it along a ruler with moderate pressure to form parallel lines, then rotating the workpiece by 90 degrees and repeating the action. For my experiments, I will use a small creaser-like tool that I have made by removing the cut of a square rifle file. As foil materials, I will use tin foil (0.03 mm) as well as sterling silver foils of different thicknesses (0,025 mm to 0,04 mm).

Using foil for stone securing

Not a small number of foils seem to have a further purpose: In many cases, the foils are trapped between the stone edges and the surrounding metal of the setting. Is it possible to hold a stone in place with the foil?

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Fig. 9: Disc brooch, Hürth-Kalscheuren, LVR Landesmuseum Bonn XV (photo: RGZM/Stempel)

If times permits, I would like to produce a foil in the way outlined above using a fire-gilded silver foil. In the next few weeks, I will report about my experiments and I am curious about the results and your comments.

 

Featured image: Buckle, Endre socken, Statens Historiska Museet Stockholm 484:12, detail: garnet cloisonné with foils behind the garnets. (photo: RGZM/Stempel)

Auf der Suche nach dem Karfunkelstein. Granatabbau und Verarbeitung im heutigen Rajasthan, Indien.

Dr. des. Borayin Larios, Ruprecht-Karls-Universität Heidelberg

talks about his field trip to India where he was searching for garnet mines and gemstone cutters in contemporary Rajasthan.
In this region garnet has been mined already in the early Middle Ages when it found its way to Europe.

Dienstag, den 11. Oktober, 18.15 Uhr

Römisch-Germanisches Zentralmuseum – Vortragssaal

In diesem Vortrag werden die Ergebnisse der im Jahr 2014 durchgeführten Feldforschung in Rajasthan, Indien im Rahmen des Projektes „Granat in historischen und archäologischen Quellen aus Südasien“ vorgestellt. Dabei wird versucht durch eine systematische Suche nach archäologischen und historischen Zeugnissen in Südasien den Weg des Edelsteins von der Mine bis zum Hafen nachzuvollziehen. Das Material, welches hier vorgestellt wird, dokumentiert, unter anderem, die Abbauquellen für Almandin-und-Pyrop-reichen Granatstein, so wie auch die rezenten und traditionellen Verarbeitungstechniken von Granat in regionalen Minen in den Distrikten Tonk und Ajmer und Edelsteinschleifereien in der Hauptstadt Jaipur. In dieser Region wurde bereits im frühen Mittelalter Granat abgebaut, der seinen Weg bis nach Europa fand. Das indologische Forschungsprojekt ist am Südasien-Institut der Universität Heidelberg beheimatet und Teil des „Weltweiten Zellwerk“-Projekts.

This is the abstract of the presentation held during the lecture series in summer/autumn 2016.

See the full program here!

Historic England in the early middle ages

RRN-logo-with-tagline
http://royalresidencenetwork.org/

The blog brings together the results of five different projects concerning early royal residencies in England between 300 and 800 AD.

In Lyminge the University of Kent is doing large-scale excavations in the area of the monastery. The site shows the patronage of Kentish royal dynasty in 7th century AD.

Rhynie is supposed to have been a early royal centre of the Picts during 5th and 6th century AD. The investigations are done by the Northern Picts project at University of Aberdeen.

“Yeavering: A Palace in its Landscape” is a project at Durham University. Through a geophysical survey the hill fort and the settlement from the 6th-7th century AD have been investigated to develop a further survey.

Sutton Courtenay/Long Wittenham is supposed to have been a centre of the early West-Saxon Kingdom which emerged by the 7th century AD. The project is coordinated by Helena Hamerow of University of Oxford, who kindly held a lecture at our “Gemstones in the First Millenium” conference.

Rendlesham, five miles from Sutton Hoo burial site is examined since 2008 by metal detecting to investigate the East Anglian royal settlement from 5th to 8th century with support from various institutes.

Garnet brooches – Jewellery for women in their prime of life?

Deutsche Version

Today I would like to present to you a blog concerning different archaelogical topics: “Archaeologiskop” by Dr. Doris Gutsmiedl-Schümann.

In particular one post is of special interest for the topic of our blog.  The post is titled: “Auf den Spuren unserer Vorfahren: Archäologie frühmittelalterlicher Gemeinschaften am Beispiel der merowingerzeitlichen Bevölkerung von Aschheim, Lkr. München” and was published 06/25/2015.

Blogpost by Doris Gutsmiedl-Schümann

It deals with an early medieval cemetery on the countryside near Munich with ca. 450 burials dating from ca AD 480  to ca AD 680 . By analysing the finds and including the anthropological data, like sex and age of the deceased, Doris Gutsmiedl-Schümann could show a distinction of grave goods varying with the age of the deceased. With respect to our project the observations regarding garnet brooches are of special interest. These were obviously limited to women who have reached the high point of their social development.

Read the full blogpost here: http://archiskop.hypotheses.org/61

Granat -Fibeln: Schmuck für die Frau in den besten Jahren?

 

Hier möchte ich auf einen Blog aufmerksam machen, der verschiedene archäologische Themen behandelt: Archaeologiskop von Dr. Doris Gutsmiedl-Schümann.

Besonders ein Beitrag ist im Kontext unseres Forschungsprojekts interessant. “Auf den Spuren unserer Vorfahren: Archäologie frühmittelalterlicher Gemeinschaften am Beispiel der merowingerzeitlichen Bevölkerung von Aschheim, Lkr. München” wurde am 25.06.2015 veröffentlicht und behandelt das frühmittelalterliche Gräberfeld Aschheim-Bajuwarenring im Kreis München.

Blogpost by Doris Gutsmiedl-Schümann

Dort wurden ca. 450 Gräber aus der Zeit zwischen ca. 480 und 680 nach Chr. gefunden. Unter Einbezug der anthropologischen Ergebnisse wie Geschlecht und Alter der Bestatteten konnte Doris Gutsmiedl-Schümann Unterschiede in den Grabbeigaben respektive des Alters der Verstorbenen. Von besonderem Interesse für den Kontext unseres Forschungsprojekts erscheint mir die Erkenntnis, dass Schmuck mit Granateinlagen erst bei Frauen in fortgeschrittenem Alter vorkam, die den Höhepunkt ihrer sozialen Stellung erreicht hatten.

Der komplette Beitrag hier: http://archiskop.hypotheses.org/61

 

 

 

Garnet jewellery in Norway: The Norwegian disc-on-bow brooches and Viking memories

Ann Zanette Tsigaridas Glørstad & Ingunn Marit Røstad,  Museum of Cultural History, Oslo

The continental tradition with the use of garnets in jewellery from the early Middle Ages spread north up to Norway during the 6th and 7th centuries, albeit used in a much lesser degree. Garnets are, however, frequently used in the so-called disc-on-bow brooches. These are one of the most spectacular jewellery types we know of from this period in Scandinavia. They are usually made of gilded copper alloy and the surface is covered with garnets set in cloisonné technique. The manufacturing of the brooches take place in the period between c. 550–800 AD, i.e. the period leading up to the Viking Age. However, many of the brooches have been found in Viking graves, and are thus quite old when buried. How is this phenomenon to be understood?

This is the abstract of the presentation held during the lecture series in summer/autumn 2016.

See the full program here!

Archaeogemology and ancient literary sources on gems

Lecture held by Lisbet Thoresen, Temecula, CA

Archaeology and discoveries of new gemstones and new gem sources in recent decades attest to the need for critical review and updating of literature in translation concerning gems of the ancient world. The origins and identities of gemstones used in ancient glyptic have been inferred almost exclusively from literary descriptions available in secondary or even tertiary sources after now-lost ancient original texts. To date, no epigraphical or philological study has verified the ancient gem cutters’repertoire of materials against empirical gemological examination of extant material in public or private collections. However, such objective data should improve interpretation of literary source material that is often fragmentary or contains descriptions fraught with lexical ambiguities and contradictions. A carefully qualified perspective is needed. Whether in original form or in translation, manuscripts, from antiquity to the present day, reflect some degree of current knowledge about geography and gems in the contemporary world of the author/epigrapher/translator. Contemporary knowledge attributed to earlier cultures is an unwitting bias that frequently eludes both translators and scholars. Together with critical examination of the imprint of authorial bias, a gemological review of extant material is discussed in relation to the important treatises on gemstone nomenclature, identity, and geographic origin.

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).

Gemstones in pre-Islamic Persia: Selection and meaning of material and shape of Sasanian seals

Lecture held by Nils Ritter, Berlin

One of the most common class of artefacts of pre-Islamic Persia are gemstones, which were used as seals as well as jewellery. So far, almost 10.000 seals from the Sasanian period are known, whereas few material is known from the preceding Parthian period, yet.
Centred in Persia, the Sasanian dynasty ruled from the Euphrates to the Indus, holding a position of supremacy for more than four centuries (from AD 224 to 652). Their gemstones respectively seals have had the highest geographical and social distribution of all known periods of pre-Islamic Persia.
The Sasanians chose colourful gemstones of different shapes, predominantly made of microcrystalline varieties of quartz. They stand out in the art of seal-cutting of the late ancient world not only for their quantity and distribution, but also in the character of themselves: this class of artefacts is significantly standardized in material, colour, shape, imagery, style and cutting techniques.
In the present paper, I will focus on the selection, background, and meaning of the materials, the colours and the shapes of Sasanian seals in order to present the traditional and innovative values of this class of material culture.

Lecture held during the conference “Gemstones in the first Millennium AD. Mines, Trade, Workshops and Symbolism.” October 22nd, 2015 at the Roemisch-Germanisches Zentralmuseum, Mainz (Germany).

Gems and precious stones from the Bible to the Liber Pontificalis.

Their combination, colours and contexts.

Lecture held by Michelle Beghelli, Mainz

This paper aims to explore some lesser-known uses of gems, with a special focus on the Early Middle Ages (7th-9th centuries) and on liturgical contexts. In order to do so, the data conveyed by the written sources and the material evidence have been gathered and compared. The altar with its surroundings – the sanctuary – has been chosen as the underlying theme to approach the subject.  This was the most sacred area in a church, where only the clergymen were allowed to be, and where every object was highly charged with symbolic value. The gems used in this context have also their own allegoric meanings: in the Bible itself they are constantly mentioned, although they are associated with both the holiest and the most evil figures and things. Their “positive” symbolic connotations were, however, one of the main reasons why they were employed in decorating Early Medieval liturgical items – together of course with their ornamental value and their meaning as an indicator of the economic and political power of the Church –. The objects preserved in the museums and the written sources offer a rich documentation about the types and the combinations of precious stones which were used to this purpose. The scientific literature on chalices, patens, crosses, reliquaries, hanging crowns with gem inlays is abundant, and at times it has been possible to detect some ancient restorations. A little known written document, however, offers additional, precious information on how these restorations could be performed in the 9th century. The same source includes a small enigma about diamonds, for which a possible solution will be proposed. Other contexts of use of gems have also been little inquired, namely their employment in the stone liturgical furnishings (altars, chancel screens, etc.) and in the icons with depictions of saints. Despite the evidence is scattered, a collection of various pieces of information allows to shed light on these last aspects.

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).

The Color and Material of Greco-Roman Magical Gemstones

Lecture held by Christopher A. Faraone, Chicago

In the Roman Imperial period inscriptions and new iconography appear for the first time on gems manufactured in the Mediterranean basin that clearly indicate these gems are being used as magical amulets. In the past scholars have argued that such amulets are a completely new phenomenon and that they reflect the sudden onset of anxiety or superstition, in the latter case brought on by closer Greek contact with “oriental” societies.  I have just completed an entire book arguing against this approach and suggesting instead that the key changes were (i) people began to inscribe on the gems words that they previously spoke over them; and (ii) they introduced new images of powerful new Ptolemaic gods such as Harpocrates or Sarapis. There were, however, also some important technical changes in the gems themselves, because in the Roman period gem-cutters began to use cheaper opaque stones of various colors, such as chalcedony or jasper, and they began to favor flat surfaces that allowed them more easily to carve figures in intaglio and text. A change, for example, from a convex carnelian to a flat red jasper. Scholars have paid close attention to the correlation between images and text on these gems, but not always to their media and in my lecture today I would like to explore the reasons why certain colors and media become important as amulets in this period. One important feature of these stones is their uncanny properties. Certain stones, for example, made a strange sound when shaken, emit an odor when rubbed, attract iron or straw or otherwise seem to straddle the boundary between the organic and the inorganic – were singled out by the Greeks as powerful and were used as amulets. In my paper this afternoon I will focus on a handful of these stones and show how the Greeks – as they were wont to do — borrowed some of these stones from the Near East (especially Mesopotamia, by way of Persia) and in other cases invented their own traditions by turning organic amulets, for instance the eyes of green lizards, into green gemstones or the use of brownish gemstones inscribed with the image of a scorpion to ward off brown scorpions.

Lecture held during the conference “Gemstones in the first Millennium AD. Mines, Trade, Workshops and Symbolism.” October 22nd, 2015 at the Roemisch-Germanisches Zentralmuseum, Mainz (Germany).

Gemstones in Indian Religions

Lecture held by James Mchugh, Los Angeles

India and neighboring regions were the main sources of many gemstones in the Old World. Pre-modern Indian texts on gemology display a complex knowledge, both practical and mythological, of the origins, locations, properties, and evaluation of many types of gemstone. In Hinduism, Buddhism, and Jainism gemstones play a number of important and varied roles, from sanctifying the foundations of temples to constituting the building blocks of heavens. This paper introduces the mythological origins and supernatural potencies of the main gemstones as found in textual sources, and also presents an explanatory survey of the main religious contexts where gemstones were used. The paper will also consider the methodological difficulties in comparing textual sources with material finds.

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).

Foto: Carvings of strings of jewels from a 6th century CE cave at Badami India. (J. Mchugh)

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.

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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.

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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.