Ten medieval brass mortars of ribbed form from British collections are described. Three have known provenances: Coity Castle, Mid Glamorgan; Manorbier Castle, Dyfed; and Deptford. The relationship of the ten with the Hispano-Moresque and Islamic series of such vessels is discussed. They have been sampled for analysis of the alloys used in their manufacture. Correlations were then sought between alloy types and stylistic features as an aid to classification; further, comparisons were made with other analytical data on medieval copper alloys. The majority of the mortars were found to be leaded bronze or so-called leaded gun-metal. The Deptford mortar was found to be made from an impure copper (98.60% copper); the Manorbier example contains 12. 40% lead, and the Coity vessel was made from a leaded brass (69.30% copper, 22.90% zinc, 7. 04% lead). -- AATA