CROWN.

In the course of a two-week campaign to perform Raman investigations in May 2022, we systematically analysed all the gemstones adorning the imperial crown for the first time. This was undertaken in collaboration with the Institute of Mineralogy and Crystallography of the University of Vienna. Until then, all the information we had for the 172 gemstones on circlet, cross and arch were handwritten notes from 1977 recording the optical classification of some of them.

WITec Wissenschaftliche Instrumente und Technologie GmbH, a private company specializing in scientific instruments, provided us with a specially-adapted Raman spectrometer that allowed us to measure both Raman and photo-luminescence spectra. Thanks to many years of experience in determining Raman in gemstones, Professor Dr Lutz Nasdala was able to identify all the stones on the crown directly while performing the measurements.

Today, the Imperial Crown is embellished with a total of 71 sapphires, 50 garnets, 20 emeralds, 13 amethysts, four chalcedonies, three spinels, and eleven differently coloured pieces of glass. Further examinations to identify the stones in more detail are planned within the course of the project. For instance, we aim to classify different types of garnets, determine special inclusion phases, and obtain information on the origins or provenance of individual stones. We will continue to only use non-destructive examination methods such as X-ray fluorescence analysis.

Martina Griesser, 4.9.2022

On the reverse of the Imperial Crown’s central cross, niello was melted into the engravings of Christ on the Cross and the accompanying inscriptions, delineating them more clearly against the gold background. Niello is a black-coloured mixture of sulphur and other metals. Early medieval sources report recipes containing the sulphides of silver, copper and lead as main components in various compositions.

Art historical research has repeatedly linked the central cross’s image of Christ with niello decorations on the reverse of the so-called Imperial Cross (Secular Treasury, Inv. WS XIII 21).  This examination thus aimed to determine whether such a connection could be confirmed with regard to the chemical composition of the respective niello decorations using energy-dispersive X-ray fluorescence analysis (XRF). We used a portable device (PART II) that was developed and built at the KHM in the course of a previous research project ("Portable Art Analyzer - PART", project no. L430-N19, funded by the FWF). It allows focusing on the niello’s very fine lines due to its measuring spot of about 150µm.

The results of this analysis show that the niello masses of the crown’s central cross are composed of silver-, copper- and lead-sulphides as well as possibly a small trace of gold, which could come from the silver. In contrast, the niello on the Imperial Cross consists only of silver- and copper-sulphides. Only traces of lead and gold are detectable here, probably due to material impurities. At least from the perspective of the material sciences, such different formulations do not immediately corroborate a direct workshop connection between the two works.

In the further course of the project, we will continue to evaluate this data, qualifying and contextualising it with literature on the making and composition of niello in the Early and High Middle Ages. Moreover, the close examination of the goldsmith’s technique and tool marks on the crown`s central cross, made possible at an unprecedented level by the use of 3D-digital microscopy, might also provide further insight.

Katharina Uhlir, Teresa Lamers (October 18, 2022)

The portable X-ray fluorescence device PART II, already used for the analysis of niello [link: Material Analysis / Analysis of the Niello Decoration], was used in spring 2023 to investigate the chemical composition of gemstones, pearls and enamels of the Imperial Crown as well as the gold composition due to its small measuring spot of only about 150 µm. Of particular importance for enamel analysis is that the measuring head of this instrument can be evacuated. This allows the detection of light elements with low atomic numbers - such as sodium (Na), magnesium (Mg) and aluminium (Al) - which are essential for the determination of enamel composition. At the same time, however, the small working distance of only 1 mm is often a hindrance due to the strongly three-dimensional structure of the imperial crown, and therefore not all details to be investigated are always accessible with this device. Despite this limitation, it was possible to carry out a large number of analyses, in the interpretation of which it was possible to include preliminary investigations that had already been carried out in 2014, as they formed a valuable basis for the further investigations.

In addition to areas representative of the different coloured enamels, areas attacked by corrosion or those with unclear characteristics were also analysed. Overall, the following observations were made, although the complete evaluations will still take some time:

• Most enamel colours (green, light blue, dark blue, turquoise blue and brown-red) are of the soda-lime type. The incarnate and the yellow enamel are basically also of the soda-lime glass type, but in contrast to the aforementioned colours, they have clear additions of lead oxide (PbO). The enamel of the potassium glass type includes black and brick-red enamel. The K₂O content of these glasses is approx. 10 and 16 percent by weight respectively. The CaO content (stabiliser in the glass) is very high and lies at 12-15 percent by weight. Nevertheless, the black enamel proves to be very unstable and shows the most conspicuous signs of corrosion. Initial analyses of the corrosion products with the scanning electron microscope (SEM) showed the presence of calcium, sodium, potassium and lead compounds (chlorides and probably carbonates or salts of organic acids). Further investigations into corrosion and its cause using µ-raman spectroscopy and SEM are planned. For enamelling technology, it is of interest here that potash glasses have a higher melting point than soda-lime glasses.
• For the pearls at the crown and cross and the large pearls of the bow, a differentiation between freshwater and saltwater pearls can be made well with XRF by comparison to reference materials based on characteristic detected elements and their relationship to each other.
  [link: Material Analysis / Examination of the pearls].
• The investigation of the gold compositions was unfortunately limited by the severely restricted accessibility to the areas of interest. Nevertheless, it will be attempted to make comparisons of the individual gold alloys as far as possible and to determine technological correlations between different structural elements and alloy compositions. The comprehensive evaluations required for this are currently still in progress.
• An imitation gemstone examined on the temple shows a high barium content. Glasses of this type were first produced in the early 19th century, so the XRF analysis greatly limits the time span for the replacement of the original stone with the imitation at this point.
• The gemstones accessible for analysis were also examined in order to obtain further clues as to their exact classification and provenance or to substantiate assumptions in this regard.

For a comprehensive interpretation of pearls, gemstones and enamels, further investigations with various spectroscopic and photographic methods are planned.

Katharina Uhlir, Martina Griesser (24.7.2023)

The Kunsthistorisches Museum’s Conservation Science Department owns a Bruker CRONO macro-XRF scanner. A macro-X-ray fluorescence scanner (MA-XRF) carefully maps larger surface areas ‘pixel by pixel’ (max. 60 x 45 cm), taking an X-ray fluorescence spectrum for each data point. Together these spectra reveal key compositional information, including, for instance, the distribution of copper on the analyzed surface – on the enamel plates of the Imperial Crown it is present in blue, turquoise, green and red enamels.

In addition, the Bruker CRONO allows us to perform individual measurements at selected data points, similar to the PART II system described earlier [link: Material Analysis / Examination by means of µ-X-ray fluorescence analysis]. The collimator options are 0.5 mm, 1 mm, and 2 mm diameter, providing elemental data from a much larger data-point than that using a µ-XRF. Compared to the µ-XRF system PART II, the CRONO scanner can take measurements from a greater distance (1 cm), facilitating the mapping of data points on three-dimensional objects. At the same time, however, aerial absorption of signals from elements with a low atomic number (esp. sodium, magnesium, phosphorus, and aluminum) is especially problematic when analyzing enamel.

In May and June 2023, the following analyses were carried out, but their comprehensive interpretation will require some time:

• mapping of the enamel pates: despite the enamel plates’ convex shape, the distribution of the characteristic elements responsible for color in the different enamels is clearly represented; we were able to document the distribution of a not-yet-identified dark leaded substance
• small areas of the cross were scanned in order to define the individual zones of the different metal alloys at the solder joints. A scan of the niello decoration revealed inhomogeneities and varying thicknesses of the different layers
• high-resolution scans of both sides of the arch were an attempt to determine whether the countless tiny pearls are freshwater or saltwater pearls; however, the procedure proved unsuitable
• in addition to our earlier analyses using the PART II system, some of the gold areas were analyzed using the CRONO’s point measurement mode. Despite the much-improved access to several data points, a number of interesting points could still not be investigated regardless of the increased distance between the XRF system and object
• the metal components of the case were analyzed to determine the comparability of its individual parts
• as preparation for comparative measurements of objects in Germany (Cologne, Essen, Munich) point measurements of the enamel on the Imperial Crown were carried out using parameters determined in collaboration with the Rathgen-Forschungslabor, in order to optimize the comparability of results of investigations undertaken with different measuring devices (CRONO MA-XRF scanner in Vienna, and ELIO scanner in Germany)

Katharina Uhlir, Martina Griesser (24 July 2023)

The second research campaign (9 January - 23 June 2023) focused on analysing the chemical composition of the different materials that make up the Imperial Crown. Precise knowledge of the chemical composition is an essential basis of conservation science research. It enables conclusions to be drawn about specific material properties and about ageing and corrosion processes. Likewise, the results of analyses can provide clues to the origin (as in the case of precious stones) or be used to determine the species (as in the case of pearls).
[link: Material Analysis / Examination of the pearls]

However, the analysis possibilities are limited by the mandatory requirement of non-destruction (no sampling) and mobility (equipment must be transported to the crown - not vice versa). The three-dimensional structure, especially of the gold surfaces, is a further, strongly limiting factor in the investigations. The relatively large measuring heads of the analysers have to be brought very close to the surface. This is only possible at isolated points on the crown, which limits a complete and systematic examination of the gold alloys from the outset. The enamels, with their only slightly curved flat surfaces, offer better measuring conditions.

By using different, complementary optical and material-analytical examination methods, we are trying to obtain as broad a spectrum of information as possible in order to deepen our knowledge of the materiality, the state of preservation and the complex corrosion processes.

Within the project, the enamels of the Imperial Crown represent a main topic of conservation science. Enamel is not a stable system. It is particularly subject to chemical or physical processes that take place on a micromolecular level within the enamel layers and become visible over time as signs of decay. Changes in appearance in the form of white, crystalline efflorescence were also observed on the sinking enamels of the Imperial Crown. A particular feature of the enamels of the Imperial Crown is the strong inhomogeneity of individual colours as well as the enforcement of the surfaces with a multitude of semicircular holes that were created during the manufacturing process (trapped gas bubbles that migrated to the surface during the melting of the enamel in the kiln). Point measurements cannot adequately characterise the chemical composition in this case. However, with the macro X-ray fluorescence scanner it is possible to record spectra from the entire surface, map and display the elemental distribution.
[link: Material Analyses / Further material analyses using the macro-XRF scanner CRONO]

The great challenge for conservation science will be to interpret the results obtained from the measurement data to understand what they mean for the corrosion processes, what conservation measures need to be taken and what consequences need to be drawn in terms of optimising the storage conditions to ensure the long-term preservation of the crown.

Helene Hanzer (20. 7. 2023)

Today, circlet, arch and cross are decorated with a total of 233 pearls. In addition, there are about 600 smaller pearls arranged to form the letters on the arch. Pearls - also classified as organic gemstones - are a material that, like mother-of-pearl, is produced within certain types of molluscs by biomineralization processes. Thin layers of calcium carbonate crystals (aragonite, calcite or vaterite) are built up over an organic cell nucleus, creating a characteristic terrace-like structure that is responsible for the special lustre effects of pearls. Dr. Stefanos Karampelas from the Laboratoire Français de Gemmologie (LFG) Paris, an internationally renowned expert, kindly agreed to examine the pearls on the Imperial Crown.

The research project aims to describe each pearl and determine whether it is a saltwater or a freshwater pearl. This is made possible by material analytical investigations using X-ray fluorescence analysis (µ-XRF, device: PART II). The main difference in the chemical composition of saltwater and freshwater pearls is the ratio between strontium and manganese. Other characteristics are size, shape and lustre.

Initial results show that the majority of pearls used on the crown are saltwater pearls. In classical antiquity and the Middle Ages, they mainly originated in the Persian Gulf and came to Europe via various trade routes. Some of the pearls on the Imperial Crown are exceptionally large (circa 8-12 mm); they are among the largest specimens known in Europe before the discovery of America, and must have been extremely rare and costly.

Unlike gemstones, pearls are delicate and easily damaged, fractured or affected by other aging processes. Many of the pearls were (re-)attached with wires during later repair work on the settings. We may therefore assume that not all the extant pearls can be traced back to the time the crown was created. Based on the findings of optical examinations, we hope to determine which pearls are original and which are later replacements.

Teresa Lamers (24 July 2023)

The inscriptions on the enamel plates of the Imperial Crown have recently attracted increased attention from historians. In connection with certain letter shapes on the enamel plates, they argued that the crown could not have been created before the late 11^th century. As a result, the CHVONRADVS named on the arch is said to have been King Conrad III (r. 1138-1152), who is subsequently also identified as the crown’s commissioner. The suggested dating is very different from that found in art historical scholarship.

Within the framework of this project, all inscriptions on the crown will be examined together with exact technological observations for the first time and the findings discussed in a direct interdisciplinary exchange.

The crown has a total of ten inscriptions. They are fashioned in four different techniques and placed across seven different components of the crown: we find both cloisonné and champlevé enamel on the four plates of the circlet, niello on the back of the central cross and, in a technically unusual form, another inscription is formed by the small threaded pearls on both sides of the arch. We aim to examine epigraphically significant aspects of these inscriptions from all angles, both in terms of their respective characteristics as graphism on the one hand and as text on the other. With regard to the graphic execution, it is not only about the style of the writing (palaeography) and its historical classification, but also about its semantic implications. The latter also concerns the arrangement of the writing and conventions of its relation to pictorial depictions. In the case of the texts, we are focusing on linguistic and orthographic circumstances as well as questions of intertextuality (relationship to other texts).

Because of this, knowledge of relevant written sources and their respective reception history is also of great importance. For instance, the texts of the banderols on the enamel panels have repeatedly been associated with the Imperial coronation liturgy in scholarly literature. Central objectives of the present analysis surrounding the inscriptions are the chronological and geographical classification of the crown and its components, combined with an effort to gain a deeper understanding of its semantic significance.

Clemens M. M. Bayer (November 23, 2022)

What significance might arise from historical representations of the Imperial Crown in the context of the project’s objectives? This is the central question guiding the research into the pictorial sources for this project. So far, the literature has focused primarily on identifying medieval representations of the crown. Often these pictorial sources were used to historically contextualise the shape and individual design elements of the Imperial Crown.

However, none of these images can be established with complete certainty as a representation of the Viennese crown for the period before 1500. This led to exceedingly controversial discussions of these examples in the literature. Even if a compilation of these representations hardly promises new insights for the concrete questions of the project, their systematic documentation is nevertheless planned.

Likely made as a preparatory study for his idealised portrait of Charlemagne, Albrecht Duerer’s famous drawing of the Imperial Crown (after 1510), provides a turning point in the way that the crown’s objecthood and materiality are represented. Taking into account this new approach towards more naturalistic representations in the visual arts in general, we decided to focus our research on images from the period after 1500, recording and evaluating as much material as possible. Since May 2022, around 16,000 entries in national and international image databases have been systematically searched and assessed. Based on these efforts, about 550 entries have so far been created in an internal CROWN database.

A detailed evaluation of these entries is still pending. However, one finding we can already ascertain is that while the Imperial Crown was frequently depicted after Dürer, this was rarely done in such detail that a concrete preservation state of the object could be deduced from the images. Notable exceptions like the engravings by Johann Adam Delsenbach published in 1790, the illustrations from a magnificent work by Franz Bock commissioned by Emperor Franz Joseph I and photographic prints from the early 20^th century in the holdings of the Kunsthistorisches Museum in Vienna, however, indeed promise new results for the questions of the project.

Evelyn Klammer (November 18, 2022)

In addition to the systematic collection of pictorial sources, we also aim to collate written historical accounts of the Imperial Crown. This will form a foundational pillar for an interwoven understanding of the object’s material history and, ideally, allow us to trace its present condition back through time. Written sources from the time the crown was deposited in Nuremberg (1424-1796) have never been systematically sifted and evaluated in relation to the crown’s present appearance and object history. An initial survey reveals that they provide valuable insight into historical repairs and interventions.
In contrast, the collection of written sources from the time before 1400, suggests hardly any new insights in this respect. This material has already been researched and debated many times. Nevertheless, we are preparing a carefully curated catalogue of these sources. Our aim is to provide a solid foundation and comprehensive account for further discussions of the crown’s fates in the Middle Ages.

A number of references in Karl-Engelhardt Klaar’s essay on the ‘Sicherung und Pflege der Reichskleinodien in Nürnberg’ (in: Nürnberg – Kaiser und Reich, exhibition organized by the Staatsarchiv Nuremberg, Nuremberg 1986, pp. 71-82) suggested a review of early modern archival material in the Staatsarchiv Nuremberg that was likely to contain information on the use, safeguarding and maintenance/repair of the Imperial Crown and the other artefacts comprising the imperial insignia. With the help of Archivoberrat Dr Daniel Burger, we were able to examine and record the material at Nuremberg in February 2023.

Next, Pia Metschitzer (a historian working in the KHM Archive) began to produce transcripts for our project. The sources edited so far include very interesting remarks documenting both extant and missing parts of the stone- and pearl decoration, and repairs. We have notes dating from 1521, 1612, 1619 and 1630 respectively that document audits of the crown’s components. In 1619, the audit seems to have been carried out following the coronation of Emperor Matthias I and his consort, Anne, and Hans Beutmüller (died 1622), a goldsmith first recorded in Nuremberg in 1588, was asked to evaluate the crown. Beutmüller’s appraisal includes two straightforward drawings (presumably also by him) that document the positions of the different stones decorating the various parts of the crown at that date.

Also important are receipts for payments for individual repairs carried out on the Imperial Crown in the seventeenth and eighteenth century; most, however, do not dwell in detail on the actual work and can therefore not be connected to specific interventions, but they prove that such repairs were carried out.

Franz Kirchweger (28 Sept. 2023)

In the course of our comprehensive examination of the Imperial Crown using 3-D digital microscopy [link: Technological Research / Investigation using 3D digital microscopy], we were able to photograph two previously unknown ancient intaglios included in the stone decoration. The obverses of the two engraved gems face inwards, which is why they are not visible from the outside under normal conditions.

The amethyst positioned in the lower row of the front plate (A) on the left shows a harbour scene with ships; the engraved gem set in the lower row of the back plate (E) depicts a half-length maenad holding a theatre mask. The examination was carried out by Prof Erika Zwierlein-Diehl of the University of Bonn, a leading international expert on ancient glyptic art and its afterlife who has published numerous works on the ancient gems and cameos in the Kunsthistorisches Museum.

According to her preliminary research, the intaglio featuring a maenad is the earliest and most beautiful version of a type of which only a few examples have come down to us. It is the work of a Greek master active in the middle or third quarter of the first century B.C, i.e. during the transition from the late Hellenistic style to Augustan classicism. The gem showing a harbour scene was executed in the so-called miniature style and produced sometime between the end of the first century B.C. and the first century A.D. It is the most detailed example of the twelve extant cameos featuring harbour scenes.

Franz Kirchweger (28 Sept. 2023)