Correctly known as a smithing hearth cake, quite literally a load of old rubbish. These form at the bottom of a blacksmith's hearth from residual slag in the worked iron and ash from the fire. This example is 9x7cm and has a mass of 207g, making it a relatively small hearth compared to other examples. It has a concave base in which we can see iron staining and a highly irregular top which shows some incorporation of charcoal. Ours was found in modern Staines, Roman Ad Pontes at the County Sports site. Significant amount of slag were found here, suggesting a collection of smithies. Source: Objaverse 1.0 / Sketchfab