January’s line on the birthstone calendar carries one name, garnet, and has never carried another. Why the deep red stone got the coldest month is unrecorded. Where the stones themselves came from is a different sort of question, and that one now has partial answers.
The goldsmiths who set garnet into gold across early medieval Europe left no account of their suppliers. For most of the twentieth century that closed the subject, since a stone with no paperwork has no history beyond the object it sits in.
Then the stones turned out to be readable. Garnets from one deposit carry a mix of trace elements and mineral inclusions unlike the mix from another, because they grew in unlike rocks. Read the proportions and you have something close to a signature, which can be matched against material from a deposit somebody has already sampled.
Reading a garnet without taking it out of its setting
The obstacle was never the chemistry. It was that reading the chemistry used to mean prising the gem out of its mount, which nobody was ever going to permit on an object like the Sutton Hoo purse-lid.
Particle-induced X-ray emission removed the objection. A high-energy ion beam is aimed at the stone where it sits and the elements in it fluoresce, each at its own wavelength. The object goes back into its case unaltered. What had been a destructive test became something a museum could run on its own most valuable holdings.
What the beam cannot do is name a mine. It reports proportions, and proportions have to be compared against reference material from deposits somebody has already sampled, which means the map is only as complete as the sampling behind it. A garnet from a source nobody has characterised comes back as an unfamiliar signature rather than as an answer.
The British Museum ran the beam over five garnet-set objects for its Silk Roads exhibition and reported that all five “were decorated with gems from India, Sri Lanka and Czechia”. It went further and broke the results down. Four of the objects combined garnets from at least two geographical sources; on the fifth, an imitation buckle, the stones analysed “appeared to come exclusively from India”.
Then the museum said, in its own voice on the same page, that “The final, fully analysed results are still to come”. A public exhibition page that publishes a result and marks it provisional in the same breath is doing something unusual.
The supply chain behind a Staffordshire field
Birmingham Museums Trust, which cares for the Staffordshire Hoard, states the position on its own page about the science of the collection. “So far we have counted over 3500 individually cut and mounted garnets in the hoard. There are two sources of garnet in the hoard. The very small garnets came from the Czech Republic and the larger cut garnets are from the Indian subcontinent.”
More than three and a half thousand stones, every one cut to shape before it was set, reached early medieval England from central Europe and from South Asia. Read as a logistics problem rather than as a sentence about jewellery, that suggests a supply line running from Bohemia to the Indian subcontinent and terminating in a workshop making fittings for weapons.
The objects those garnets went into are what the method is being applied to. The British Museum dates the Sutton Hoo shoulder-clasps to the late sixth or early seventh century, and of one of them, museum number 1939,1010.4.a, its catalogue says that “The rectangular plate contains a central panel of fifteen cloisonné cells filled alternately with millefiori glass and garnets”, with the garnet cells “underlaid with stamped gold foil”. Somebody stamped a pattern into gold sheet and laid it beneath the stone, relying on light passing through the garnet and returning off the foil. That is a lighting decision, made around AD 600, and it only works if the stone is clear enough to let light through.
The purse-lid from the same burial, museum number 1939,1010.2.a-l, has each lobe “inlaid with cloisonné garnet work in a step-cut design”. The technique was not confined to England. A gold mount from the Domagnano treasure, found in San Marino and dated by the museum to the late fifth or early sixth century, carries “all-over cloisonné garnet and white shell inlays”. A finger-ring from the same find shows the simpler alternative, a stepped bezel forming “a square collar for a pyramidal garnet inlay”, one stone rather than a field of them.
What these objects have in common is not a place. In Suffolk, in San Marino and, before both, in the Mediterranean workshops the technique came from, the same red stone turns up cut into flat plates and seated in gold cells, across several centuries and most of the width of Europe, in the hands of people who did not share a language. Cloisonné garnet is one of the more widely distributed decorative techniques of the period, and the analysis is beginning to explain how the material for it moved.
Earlier still, the Romans were carving it. The Metropolitan Museum’s accession 41.160.693 is a garnet intaglio of Romulus, Remus and the she-wolf, and the Met gives its date as somewhere between the second century BCE and the third century CE, a window worth leaving as wide as the museum leaves it.
Where the method stops
Francois Farges, publishing in American Mineralogist in 1998 on the Merovingian garnet cloisonné in the Louvre, placed one of his garnet types in the Podsedice area of Bohemia. He was considerably more careful about the rest. “The possible presence of Sri-Lankan garnets in Merovingian jewelry is controversial”, he wrote, while holding that Sri Lankan sources “remain highly plausible”. Of another group he named India, Sri Lanka, Central Europe and Scandinavia as the most likely origins, then added that “it is not possible here to constrain these origins more accurately”.
A quarter of a century separates that paper from the British Museum’s beam, and the direction of travel is legible: the central European end of the material is the firmest, while the South Asian end is strongly indicated and still being pinned down. A reader who wants one confident sentence about where Europe’s early garnets came from is asking for something the evidence has not yet produced, and the researchers are the ones saying so.
A second limit is about what a result means rather than how precise it is. Knowing that a garnet grew in India does not establish that it was cut there or that it arrived in one lifetime. Stones outlast the people who move them and they are reset, so a seventh-century object can hold a fourth-century stone without anything in the chemistry saying so. The beam dates the deposit, not the journey.
The mineral itself asks for very little explanation. The Handbook of Mineralogy files almandine and pyrope as members of the garnet group, gives almandine the formula Fe2+3Al2(SiO4)3 and pyrope Mg3Al2(SiO4)3, and puts both at 7 to 7.5 for hardness, hard enough to wear daily and soft enough to cut without heroics. Its name note for almandine reads: “For Alabanda in Turkey, a cutting center in antiquity.” The commonest red garnet carries the name of a town where the stone was worked rather than any place where it grew, and the gap between where a stone grew and where it was worked is exactly what the ion beam is now measuring.
The garnet group has an entry of its own in the Crystalance Mineral Library, and what crystal is for Capricorn comes at the same stone from the calendar’s other side.
January’s tradition stays undocumented and the analysis continues. The next round of results may move the map again, and the garnets will be where they have been since Sutton Hoo was buried, still in their gold, still legible.
Sources
- British Museum, Silk Roads, “From Sri Lanka to Suffolk”, for the ion-beam analysis, the three regions, the object-by-object breakdown and the museum’s own caveat: britishmuseum.org
- Birmingham Museums Trust, the science behind the Staffordshire Hoard, for the garnet count and the two source regions: birminghammuseums.org.uk
- British Museum, Sutton Hoo shoulder-clasp, 1939,1010.4.a: britishmuseum.org
- British Museum, Sutton Hoo purse-lid, 1939,1010.2.a-l: britishmuseum.org
- British Museum, Domagnano treasure gold mount, 1933,0405.1: britishmuseum.org
- British Museum, Domagnano treasure finger-ring, 1933,0405.7: britishmuseum.org
- Metropolitan Museum of Art, garnet intaglio, accession 41.160.693: metmuseum.org
- Francois Farges, “Mineralogy of the Louvre’s Merovingian garnet cloisonné jewelry”, American Mineralogist 83 (1998), 323-330, via the Mineralogical Society of America: minsocam.org
- Handbook of Mineralogy, almandine, including the Alabanda name note: handbookofmineralogy.org
- Handbook of Mineralogy, pyrope: handbookofmineralogy.org
