A Bronze Age metal hoard discovered near Dereham in Norfolk in 2019/2020 contains a rare trio of lead ingots. The objects date to the late Bronze Age, ca. 950-800 B.C., and this is the period when the hoard was deposited as well. The hoard consists of four socketed axeheads, one fragment of the cutting edge of an axe, one socketed woodworking gouge, one fragment of a sword blade, a fragment from a bun ingot and three rectangular lead ingots. Most of the objects were broken or had missing parts, and were likely buried for safety before they were melted down and reused. The gouge is the only bronze piece that was still complete when it was buried. Perhaps it had come to the end of its useful lifespan and was destined for recycling.Its the lead ingots that are the real mystery ingredient in the mix. Lead was a necessary element in bronze casting alloys, and it is found in increasing proportions by the Late Bronze Age. It is extremely rare, however, to find objects made entirely out of lead, and even rarer to find lead ingots. A handful of lead objects from Late Bronze Age hoards are believed to have been raw materials a flat sheet, irregular pieces of casting waste but deliberately shaped rectangular cakes like these have never been found before.The lead is what people are getting excited about in this particular hoard, said Dr Wilkin, who is the museums curator for early Europe (Neolithic and Bronze Age collections).The reason for this was Bronze Age metal smiths worked out the optimum recipe for casting bronze about 3,000 years ago. The combination of elements was just under 90% copper, about 10% tin and between 1 and 2% lead, he explained.That seems like an insignificant amount of lead, but if you talk to people who do experiments with bronze casting today, they say it makes a big difference to the melting point of bronze and its pourability into complex and intricate moulds, he said.A few late Bronze Age axeheads have been found with as much as 15% lead content, so the raw material could be in greater demand by the time this hoard was buried, but with no known parallels the ingots function is unclear. They could certainly have been intended to be added to the alloys when the recyclables were melted down to increase their lead content. Considering the extreme rarity of Bronze Age lead ingots on the archaeological record, however, its possible they had another purpose.Dr Wilkin speculated the discovery site at Dereham might also have been a trading post, due to its proximity to the North Sea.Theres a lot of evidence that it was quite a specialised craft and the smiths might have been itinerant and might have gone around several different communities creating tools for them, he added.The hoard is currently undergoing assessment to determine whether it qualifies as Treasure under the UKs Treasure Act, (it does; the result is a foregone conclusion). Once it is declared treasure, a valuation committee will determine its market value and a museum will be offered the opportunity to acquire it in exchange for the sum. The British Museum has already expressed interested in acquiring the hoard.