The item - a beautifully decorated tray measuring 20ins by 15ins (50cm by 38cm) - was bought by the American philanthropists Dr Raymond and Mrs Beverley Sackler for more than pounds 120,000 and donated to the museum, through its American Friends support group.
The tray - which bears a Christian inscription - is considered to be of great importance in shedding light on late Roman and early Dark Age Britain, and on early British Christianity. It goes on display in the museum today.
The testing took place following disagreement last year within the museum's Board of Trustees over the proposed purchase of the tray, said to be an 18th-century recast version of the original. At least one trustee doubted the recast treasure's authenticity.
The tests have now confirmed that it is a recast version of the original Roman tray - remade from moulds taken from the original and using the original silver. The original, made in Britain in the fourth century AD, was found by farm workers in 1729 in Risley Park in Derbyshire. However, until last year when it was taken into the London antiquities dealer Seaby's by a Midlands farmer who owned it, archaeologists believed it had been lost in the mid-18th century. Now scholars believe that the tray was recast because the original was too corroded to restore conventionally. The tray is one of only three large items of silverplate known from Roman Britain, and is richly decorated. Scenes depict hunters, people playing flutes, and shepherds. An inscription reveals that the tray was a present from a bishop to a church on an estate belonging to a man called Bogius. As such it is the only sizeable piece of Romano-British church plate ever found.
It is thought the early Christian owners of the tray lived near where it was discovered. Topographical, archaeological and place name research suggests that the church and estate of Bogius was located near Risley, and that the bishop gave greater treasure to the local Christian community than a silver tray.
A map made in 1722, before the tray was found, refers to the area as Silver Hill.
Also, the inscription on the tray refers to it as having been a donation from a bishop Exuperius, and an enigmatic piece of local history hints at the possibility that other high status items of silver treasure bore his name.
At the time when Exuperius gave the tray to the church of Bogius in the fourth or fifth century, the name Exuperius was fairly common. But in Britain by the medieval period the name had disappeared except in one place - Derby, just seven miles from Risley Park. In 1580, the bailiff (joint mayor) of Derby, a Mr Turner, decided to christen his son Exuperius. From then on until the 19th century, according to research by the Derby Museum historian Maxwell Craven, the Turners clung to this unusual name, with Turners in most generations being christened Exuperius in 1608, 1648, 1685, 1725, c1735, 1750 and 1825. The last known Exuperius Turner died in 1908.
But what of Bogius? Just one and a half miles north of Silver Hill is a farm, Boyah Grange, which may have been the site of Bogius's estate centre. A manuscript of 1200 refers to Boyah as Boyhag, which meant 'Boie's enclosure', and the Celtic version of the Latinised name Bogius, was, research suggests something like Boii, Boie or Bogi. Traces of the church may also have survived. Near to Silver Hill, in the 1950s and 60s, in an area now developed as a commercial game shooting venue, local people found fourth century Roman pottery and possible Roman building materials. The church on Bogius' estate probably formed part of the bishopric of Letocetum (now Wall, near Lichfield).
Research just published by Leicester University Press in a book called Pastoral Care before the Parish concludes that Letocetum was the seat of a major bishopric by the fifth century.
In the mid-seventh century the bishop's seat moved two miles away to Lichfield, and research has revealed that at least by the ninth century Risley was under the spiritual jurisdiction of an official - known as a prebend - appointed directly by the bishop, and that several local manors were held by the bishop.
It seems likely therefore that the generous Exuperius was a fourth- or fifth-century Romano-British bishop of Letocetum, and that Bogius's lands were originally an episcopal estate centred near Risley Park, and that the silver tray formed part of a much larger treasure, the fate of which remains unknown.