Plano-convex ingot

Plano-Convex ingots, also known as bun ingots, are lumps of metal, circular in plan with a flat or slightly concave top and a rounded base. They are most often made of copper although plano-convex ingots of other materials such as copper alloy , lead and tin are also known. Their characteristic shape is formed when molten metal solidifies within a bowl shaped cavity such as a mould or depression in the ground . Forms of plano-convex ingot are found across a wide chronological and geographical range with the first examples known from the Near East during the 3rd and 2nd Millennia BC . By the end of the Bronze Age they were found widely from North West Europe to South Asia and similar ingot forms continue in use during later Roman and Medieval periods

Manufacture

In the past plano-convex ingots have been seen as a primary product of smelting, formed at the base of a furnace beneath a layer of less dense slag .However experimental evidence has shown that regularly shaped plano-convex ingots are difficult to form within the furnace and many plano-convex ingots may have been formed outside of the smelting furnace being tapped or remelted in crucibles and cast into bowl shaped depressions or moulds.The composition and structure of the metal within some plano-convex ingots suggests that they may derive from secondary processes such as refining, alloying or the recycling of scrap metal rather than smelting.