Plano-convex ingot
Plano-convex ingots are lumps of metal with a flat or slightly concave top and a convex base. They are sometimes, misleadingly, referred to as bun ingots which imply the opposite concavity. They are most often made of copper, although other materials such as copper alloy, lead and tin are used. The first examples known were from the Near East during the 3rd and 2nd Millennia BC. By the end of the Bronze Age they were found throughout Europe and in Western and South Asia. Similar ingot forms continued in use during later Roman and Medieval periods. Manufacture Traditionally bun ingots were seen as a primary product of smelting, forming at the base of a furnace beneath a layer of less dense slag. However, experimental reconstruction of copper smelting showed that regular plano-convex ingots are difficult to form within the smelting furnace, producing only small ingots or copper prills that need to be remelted. High purity copper bun ingots found in Late Bronze Age Britain and the Mediterranean seem to have undergone a secondary refining procedure. The metallographic structure and high iron compositions of some plano-convex ingots suggest that they are the product of primary smelting. Tylecote suggested that Roman plano-convex