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High‐temperature performance of two‐layered ceramics and the implications for Roman crucibles

Roman metalworking crucibles are frequently characterised by an extra outer layer (EOL) of clay, applied to a pre-formed vessel. Three-point bending and standardised dead-weight loading tests were conducted to determine the advantages offered by the EOL. Deformation and fracture behaviour, at temperatures up to 1,100°C, of two-layer, monolithic, and tempered-monolithic briquettes were compared. Measurements indicate that the two-layer briquettes are more resistant to fracture at high-temperatures: above 850°C they show more extensive plastically deformed regions than monolithic briquettes. The influence of temper is consistent with previous results: tempering causes quasi-stable fracture and reduced fracture strength. Results suggest EOLs assisted in preventing catastrophic failure.