The Caergwrle Bowl, a decorated boat-shaped object of probable Bronze Age date, was discovered in 1823 near Caergwrle Castle, Powys. Its decorative elements include apparent representations of shields, oars and waves, executed in part by incision on gold leaf and in part by the wrappings of gold lead around a white substance identified as a mixture of romarchite and cassiterite, presumably originally metallic tin. The bowl is composed of gel-like kerogen- rich material resembling oil-rich shale that gave a poor X-ray powder diffraction pattern with lines of goethite, quartz, mica and possibly siderite and lepidocrocite. Anhydrite and hematite were detected after heat-treatment at 450 degrees C in air and were produced presumably by the dehydration of gypsum and hydrated iron oxides respectively. The source of the bowl material is uncertain, but may have been Kimmeridge oil-shale.