Experts discovered the words “Bishop Hyguald had me made” on the base of the jar, which is around 5cm high and resembles an ornate perfume bottle.
When it was discovered with the hoard in a field in Dumfries and Galloway in 2014, the jar was wrapped in textiles and when first examined it could not be seen clearly.
However, 3D X-ray imaging produced in partnership with the British Museum allowed the object to be investigated within its wrapping without damaging it and revealed there was a Latin inscription on the base.
The words, spelled out in gold letters, translate as “Bishop Hyguald had me made”.
Experts said it is the clearest evidence that some of the material in the hoard may have come from a church in the Anglo-Saxon kingdom of Northumbria, which included Dumfries and Galloway, and stretched as far north as Edinburgh and as far south as Sheffield.
However, so far nothing is known about the mystery bishop.
Professor Alex Woolf, a senior lecturer in history at the University of St Andrews, said: “The inscription is in Latin, which was the universal language of the Western Church in those days.
“The sources and records of the period are incomplete, but what we do know from them is that there were several ecclesiastics in early Medieval Northumbria with the name Hyguald.
“We don’t know of a Bishop Hyguald, specifically, but our lists of Northumbrian bishops are incomplete after 810.
“It is accordingly – and frustratingly – difficult to be more precise, but it may well be that what we’re looking at is an otherwise undocumented mid-ninth-century bishop of either Whithorn or Hexham.”
The jar is thought to have had an ecclesiastical function. The rock crystal part could have been 500 years old by the time it was wrapped in gold in the late eight or early ninth century.
Buried at the start of the tenth century, the Galloway Hoard comprised more than 100 objects, including gold, silver, jewellery, a rare Anglo-Saxon cross and textiles. It was acquired by National Museums Scotland (NMS) in 2017.
Most of it is on display at Kirkcudbright Galleries in an NMS touring exhibition supported by the Scottish Government.
However, some material that was wrapped in extremely fragile, rarely surviving textiles is undergoing careful conservation and meticulous research as part of a three-year, £1 million Arts and Humanities Research Council-funded project led by NMS in partnership with the University of Glasgow.
Dr Martin Goldberg, principal curator of Medieval Archaeology and History at NMS, said: “It looks, from the carved surface of the Galloway Hoard rock crystal, that this was once the capital of a Corinthian-style crystal column.
“This is unique in early medieval Britain, but there are parallels within the Roman Empire for objects of this type. The ones that I have seen are in the Vatican collection, where there are different forms of carved crystal columns.
“And so it was maybe 500 years old by the time it was transformed in the late eighth or early ninth century into a gold-wrapped jar.”