Gemstones on the Reliquary of the Holly Cross of Évora

This magnificent reliquary from the Cathedral of Évora, Portugal, stands out for its gemmological content and is a remarkable example of late 17th century artistry in gold, silver and gemstones to serve its liturgical objective of displaying a fragment of the holly cross of Christ.


This reliquary is believed  to keep a fragment relic of the holly cross, or holly wood, that, according to Christian tradition, belonged of the cross of Christ that was discovered in Jerusalem by Saint Helena, mother of emperor Constantin, The Great, in the 4th century. The fragment is believed to have been acquired sometime after the crusades in the 13th century and it is said to have been present the battle of Salado (1340) in southern Spain against the moors.  After its arrival in Évora in 1468, the relic was adorned with various different coloured gemstones, in other words, without diamonds (the absence of diamonds was common in that period in which this precious stone was not yet prominent in Portuguese jewellery, this situation changing radically immediately after the discovery of the sea route to India, in the early 16th century). The rich adornment of the reliquary with gemstones was made only in the late 17th century under the Friar Luis da Silva Telles, who was Archbishop of Évora from 1691 to 1703. Presently, there are nearly 1400 gemstones on the reliquary including diamonds, emeralds, rubies, blue sapphires, spinels and hessonite.

GEMMOLOGICAL STUDY

The artistic, devotional and heritage, or gemmological importance of this fabulous Portuguese gold sacred artefact led to a brief gemmological study in 2002, as part of the Artistic Inventory of the Archdiocese of Évora project, with the support of the Eugénio de Almeida Foundation, that also led to other publications. In this study, all the stones set on the reliquary have been observed, revealing their great gemmological interest, particularly in the context of the period, as will be discussed later. It is important to say that the methods of gem identification used were what is usually called “classical”, including magnification, lighting, colour filters, dichroscope, spectroscope, ultraviolet lights and thermal testers as further support. The volume of the artefact and the settings were limitations to the observation, but all the stones were positively identified and some provenance indicators were observed enabling hypothesis on their geographic origins. Advanced gemmological techniques would be critical to confirm these hypothesis, but none were used in the present study that aimed at the identification of the materials.
A gemmological study with this level of detail does not merely add value to the description of the work, but can also be important, for example, for its labelling and cataloguing for those who view this masterpiece in the Treasury of Évora Cathedral where it is on permanent display. There are other aspects of interest for which gemmological data can make a significant contribution. First of all, the data can help us reach conclusions concerning the dating of the piece. The nature of the gemstones, their likely provenance as well as their styles of cut, give us indications as to the period when they were produced, in the light of what is known of the history of the market and trade in precious stones and their cutting. This information can be an addition to other historical, artistic and documentary indicators that historians use for their research studies. Accurate knowledge of the gemstone content and their settings are of crucial importance for planning a preservation strategy and for any restoration intervention. Since there are different physical and chemical properties associated with different materials, their stability and behaviour in the presence of mechanical and/or chemical stress resulting from cleaning or restoration methods must be considered. Likewise, storage and display conditions must also take into account the factors of stability of the piece’s materials, particularly its gemstones, to ensure that their integrity and original appearance are maintained. Finally, for artefacts with many gemstones, it is necessary to assess to what extent the composition of these materials may influence their value for insurance purposes. Although in many cases historical and artistic value take precedence in the valuation of an artefact, in other cases its composition may significantly increase its value and must be taken into consideration in the valuation. Equally, the planning of the display area for the artefact, in terms of security, will have to take into account these characteristics, which constitute a factor of risk to a certain extent and this planning must be adapted accordingly. 
Before starting the study, the reliquary was inspected for missing stones or stones at risk of coming loose. Indeed, some empty settings were found and in some cases the settings themselves were missing, totalling 16. The missing stones would appear to be twelve rubies, three diamonds and an emerald. In addition to the 16 positions without stones, there are 1,374 with filled settings, which indicates that initially this jewel would have had a total of 1,390 precious stones.



GEMSTONES

The gemstone content of the Reliquary of the True Cross at Évora Cathedral is notable on several levels. It is not just that there are almost 1,400 stones, but their nature and quality, in some cases, quite exceptional. Also particularly interesting is the interpretation of this gemstone composition in the light of what is known of the precious stone market in the period to which the reliquary has been dated, the last decade of the 17th century. Gemstones of similar geographic origin are thus contextualised in this piece, as are cutting styles typical of the period.
The reliquary has 1,374 set stones, 16 less than its probable original total of 1,390, some stones having been lost over years of use. The gemmological study enabled us to identify all the stones on this work with a reasonable degree of certainty; all the stones are natural, which allows us to classify them as precious stones or gemstones, that were classified as diamonds, rubies, emeralds, blue sapphires, red spinels and hessonite garnet.
Diamond is the most abundant gem on the reliquary, in a total of 845 stones, which is a remarkable figure before the discovery of the Brazilian deposits. The most important cutting style is the rose cut, even for the larger diamonds over 2 ct, which is in line with what was used at the time of manufacture. Table cuts are present, but only in very small diamonds under 0,05 ct. Curiously, table cuts were popular for larger diamonds more than 100 years before this time when rose cuts were in great demand.

Rose cut diamonds are abundant in the reliquary. Not the large rose cut sapphire and the irregularly cut rubies set in gold. Polychrome enamels fill the silver gilt empty spaces throughout the artefact.

Rubies are present in a considerable number, 419, and the characteristics of the majority were consistent with Burmese origin, today Myanmar. Irregular cuts were described, specially for the larger stones. Emeralds are one of the most interesting gems on the implement. The 105 stones vary in size and quality and constitute a very interesting representation of the various qualities that were commercially available. From the moderately included light coloured to the eye-clean saturated top bluish-green coloured, there are representatives of almost all quality grades, serving as an extraordinary educational tool. The internal characteristics were consistent with Colombian origin. There are only two blue sapphires, but their size and cut is noteworthy as these are the largest rose cut sapphires in Portuguese collections. Two spinels were also identified, one of which had a pavillion consistent with an ancient oriental cutting style where grooves were usually made on the surface of the polished stone. The gemstone composition of the reliquary finishes with a magnificent cameo of the Ecce Homo in hessonite, an orange variety of grossular garnet.

A remarkable hessonite garnet carving of the Ecce Homo surrounded by rose cut diamonds and high quality Colombian emeralds.

By interpreting the missing stones from their position on the piece, and given the consistent aesthetic and colour language of the work, the original gemstone content of the reliquary can be extrapolated: 848 diamonds, 431 rubies, 106 emeralds, 2 blue sapphires, 2 red spinels and 1 hessonite. 


Gemstone Content and Probable Original Composition


The nature of all the gemstone materials identified is consistent with what would be expected on a piece from the late 17th century. At that time, diamond mines in India, and on a much lesser scale in Kalimantan, on the island of Borneo (now Indonesia), were active and supplied the eastern and western markets. Likewise, regions such as the present-day Sri Lanka and Myanmar were well-known and ancient producers of sapphires and rubies. Also from Sri Lanka came the orange grossular garnet known as hessonite. The spinels came mainly from the area now known as Tajikistan, from the region known at the time as Balascia or Badakhshan, although red spinels from Myanmar and Sri Lanka have also been documented. Almost certainly not of oriental origin are the emeralds which, in that period, came essentially from what is now Colombia, although there are references to the modest mines in Austria and Egypt and it is now accepted that emeralds from Afghanistan and Pakistan were already known at the time and probably also those from Davdar in China, along the silk road. Whenever it was possible to successfully observe inclusions, instrumental in a preliminary approach to determine the probable geographic origin of the gemstones, some of these situations were tested, namely for certain emeralds, rubies and sapphires which were believed to be from today’s Colombia, Myanmar and Sri Lanka, respectively. Further advanced testing could confirm these provenances.

This is, therefore, an artefact with a gem content that offers the opportunity for reflections on their unusual quantity, quality and antiquity.



Adapted from Galopim de Carvalho, R. et al. (2010) The Holly Cross of Evora´s Cathedral. Fundação Eugénio de Almeida, Évora
All images courtesy of Arquidiocese de Évora © 2010 Carlos Pombo Monteiro - Fundação Eugénio de Almeida



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