Roman metalworking crucibles are frequently characterized by an extra outer layer of clay, applied to a pre‐formed vessel. Three‐point bending and standardized dead‐weight loading tests were conducted to determine the advantages offered by the extra outer layer. Deformation and fracture behaviour, at temperatures up to 1100°C, of two‐layer, monolithic and tempered‐monolithic briquettes were compared. Measurements indicated that the two‐layer briquettes were more resistant to fracture at high temperatures: > 850°C they showed more extensive plastically deformed regions than monolithic briquettes. The influence of temper was consistent with previous results: tempering caused quasi‐stable fracture and reduced fracture strength. The results suggest extra outer layers assisted in preventing catastrophic failure.