For the first time since someone dug a hole in a Staffordshire field and buried a sack holding five kilos of glittering gold, some 1,300 years ago, the entire hoard has been reassembled far from the public gaze in a drab back room at Birmingham Museum and Art Gallery.

The Guardian was invited in to see it last week, but the assemblage can only be disclosed today, now that the gold has been safely returned to vaults and secure museum displays.

Its discovery in 2009 by Terry Herbert, an amateur metal detector living on disability benefit in a council flat, made headlines around the world. Archaeologists, who recovered more than 1,500 pieces from the field, believed they had emptied it of its treasures. Three years later farmer Fred Johnson's plough brought more gold to the surface, and a further 90 pieces, including a helmet cheek piece matching one from the original find, were recovered.

The count has now risen to more than 4,000 pieces, many of them minute. As the pieces were cleaned and conserved, more flakes of gold and tiny objects, including shirt-pin sized rivets, fell out of the clay packed around them.

Chris Fern, a specialist in Anglo-Saxon metalwork, one of the experts who has been studying the collection, has found more than 600 joins where broken pieces were once connected, jigsawed together hundreds of fragments which once decorated a magnificent helmet, and identified several pieces that seem to be the work of the same craftsman.

His work produced some surprises: one particularly beautiful gold and garnet piece, found so close to the surface that grass was growing through it, was thought to be a brooch, but now appears to join on to two other pieces to form a bizarre doorhandle-shaped head ornament.

The quality of the Anglo-Saxon gold work, with many of the pieces decorated with filigree, ribbon interlace animals with almost invisible gemstone eyes, and tiny cut garnets backed by engraved gold to make them glitter more, whose detail can really only be appreciated under a microscope, is surpassed only by the treasures of the Sutton Hoo hoard. The hoard has almost doubled the amount of filigree gold found from the period.

Another one of the 4,000 pieces in the hoard. One face resembles one of the curators at the Birmingham museum. Photograph: David Rowan/Birmingham Museums

Unlike the Sutton Hoo pieces, which came intact from a king's burial in a great ship, the treasures of the Staffordshire hoard were magnificent ruins, ornaments ripped from swords and daggers, shields and boxes, some wrenched away, some levered off with a blade – but still so beautiful that Deb Klemperer, a curator at the Potteries Museum in Stoke-on-Trent, one of the museums that joined together to buy the hoard, was reduced to tears when she first saw them.

Fern believes it may be significant that some of the worst damage was to the handful of overtly Christian pieces in the hoard, including a contorted gold processional cross, and a pectoral cross which, under x-ray, revealed a cavity under the central garnet that may once have held a saint's relic.

The pieces are overwhelmingly masculine and military – there are no women's ornaments at all – and the damage makes it almost certain that they represent loot from several places, brought together in the famously warlike kingdom of Mercia, rather than local craftsmanship.

Human details have also emerged from the work, including running repairs made on several of the pieces, such as tiny pieces of glass and amber substituted for lost garnets.

Some of the pieces were already heirlooms long before they went into the ground: the oldest, a silver-gilt sword pommel, was made in Scandinavia or northern Germany centuries earlier, and showed such heavy use that the features of the little man's face – startlingly resembling David Symons, an expert at the Birmingham museum – were almost worn away.

Some of the stars of the collection are going back on display in a recreation of a seventh-century mead hall at the Potteries Museum, complete with replica fire pit and the smell of wood smoke. Birmingham city museum is also building a new gallery to display the collection, which will open later this year.