Iron smelting slag and furnace lining
Probably Roman, 1st-4th century AD
Found during excavations by the (then) District Archaeologist at West Walk, Wickham (Soberton parish) in 1974
Slag is the name given to the waste produced when iron is smithed or smelted. This unpreposessing heap is more important than it looks, as it represents a Roman industrial site rather than just a smith's workshop. The process of extracting iron from ore has been reconstructed by analysis of the waste material, experimental archaeology and anthropology.
Cylindrical furnaces were constructed about 1-1.5m in height from clay, with small inlets at the base for forcing in air in by means of bellows, and achieving the necessary temperature (above 1250 degrees C). The furnace was preheated with lighted charcoal, then more charcoal and roasted iron ore were added through the top. The ore reduced and became iron metal, a spongy lump of small particles of iron known as a bloom, in the hottest zone of the furnace near the blowing holes. Impurities in the ore reacted to produce slag, which liquefied and flowed to the bottom of the furnace and out through an arch which would be blocked when not in use.
From West Walk, we have what was originally thought to be slag, but when analysed scientifically turned out to be vitrified ore. Also present were vitrified furnace lining and fragments of charcoal rich slag that had probably been in contact with the bloom. The runny 'tap' slag was absent, suggesting that it was allowed to cool and solidify before being raked out of the furnace. The furnaces appear to be quite small, about 0.45m in diameter. Several tonnes of waste from two slag heaps were recorded. The ore was probably obtained from the Forest of Bere, close by.
