Gemstones on the Reliquary of the Holy Cross of Évora

This late 17th century jewelled reliquary is believed to keep a relic of the holy cross, or holy wood, that, according to Christian tradition, belonged of the cross of Jesus Christ that was discovered in Jerusalem by Saint Helen, mother of emperor Constantin, The Great, in the 4th century. This fragment in particular 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, also known as battle of Tarifa, in 1340 where the armies of king Afonso IV of Portugal and king Alfonso XI of Castile fought against the armies of the Sultan of Morocco and of Yusuf I of Granada in southern Spain. After its arrival in Évora in 1468, the relic was originally adorned with various different coloured gemstones and no diamonds. The absence of diamonds in 15th century Portuguese made artefact is not uncommon if we consider that it was the discovery of the sea route to India, in the early 16th century, that brought regular shipments of diamonds to the territory. The adornment of the reliquary with many more gemstones, including diamonds, was made on a later stage in the 17th century under Friar Luis da Silva Telles, who was Archbishop of Évora from 1691 to 1703. This ca. 1698-99 reliquary was finished with nearly 1400 cut gemstones including diamonds, emeralds, rubies, blue sapphires, spinels and hessonite garnet.

Gemmological Study

A gemmological study with this level of detail does not merely add value to the description of the artefact, 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 has been on permanent display. Gemmological data may also contribute to other important interpretations, for example in what concerns the dating of the piece. The nature of the gemstones, their likely provenance as well as their styles of cut, give indications as to the period when they were produced, in light of what is known of the history of gem trade and of cutting. These informations can be additions to other historical, artistic and documental evidences that historians use in their research. Moreover, a detailed description of the stone content and their settings are highly important for planning a preservation or conservation 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 that are associated with cleaning or restoration procedures must be considered. Likewise, storage and display conditions must also take into account the factors of stability of the materials of the artefact, particularly its gemstones, to ensure that their integrity and original appearance are maintained. Finally, for artefacts with numerous gemstones, it is necessary to assess to what extent these 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 reliquary would have had a total of 1,390 precious stones.

Gemstones

The gem content of the Reliquary of the True Cross at Évora Cathedral is notable in several aspects. It is not just the fact that there is a significant number of gemstones, almost 1,400, but also 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 trade and occurrences in the period of attribution of the reliquary, the last decade of the 17th century. Gemstones and their possible geographic origin are thus contextualised in this masterpiece, as are the cutting styles typical of that period.

The reliquary has 1,374 set stones, 16 less than its probable original total of 1,390, with 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 gem materials, including diamonds, rubies, emeralds, blue sapphires, red spinels and one hessonite garnet.

Diamond is the most abundant gem on the reliquary, with a total of 845 stones, which is a remarkable count having in consideration this is before the discovery of the Brazilian deposits. The most important diamond cutting style is the rose cut, even for the larger diamonds over 2 carats, which is in line with what was used at the time of manufacture. Table cuts are present, but only in very small stones 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.

Rubies are present in a considerable number, 419, which is remarkable considering the rarity of this coloured gemstone 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 devotional implement. The 105 stones vary in size and quality and constitute a very interesting representation of the various qualities that were commercially available on that period. From the moderately included light-coloured to the eye-clean saturated top bluish green-coloured, there are representatives of almost all quality grades for this gemstone, serving as an extraordinary educational example. 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 and their date is quite interesting for that cutting style. Two red spinels were also identified, one of which had a pavilion consistent with an ancient oriental polishing 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.

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

The nature of all the gem materials identified is consistent with what would be expected on a artefact from the late 17th century which is the documented period of its manufacture. 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 with stones. Mining areas in the present-day Sri Lanka and Myanmar were well-known and referenced as ancient producers of sapphires and rubies, with Sri Lanka as a known source of orange grossular garnet, known in the trade as hessonite. Spinels of such a hue would came primarily from present day Tajikistan, from the region known at the time as Balascia or Badakhshan, although spinels from Myanmar were also known in that period. Origination almost certainly from another continent 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 to the occasional finds in Afghanistan and Pakistan and probably also those from Davdar in China, along the silk road. Whenever it was possible, inclusions were observed and documented, as these constitute a preliminary approach to determine the probable geographic origin of gemstones, namely for emeralds, rubies and sapphires, which were believed to be from today’s Colombia, Myanmar and Sri Lanka, respectively. It would be interesting to further test all of them with advanced gemmological methods to confirm of refute their geographic origin hypotheses.

 

This is a historical artefact with a remarkable gem content given its period of attribution and the fact that it has documental evidence of its manufacture, it constitutes a relevant testimony of the use of gemstones in the late 17th century and their cutting styles.

 

 

Adapted from Galopim de Carvalho, R. et al. (2010) The Holy Cross of Evora´s Cathedral. Fundação Eugénio de Almeida, Évora

Unless otherwise stated, all images courtesy of Arquidiocese de Évora © 2010 Carlos Pombo Monteiro - Fundação Eugénio de Almeida