A prism, in antique lighting, is a cut glass or crystal drop hung from a chandelier, candelabrum, lustre or wall light to catch, refract and scatter light. Although the term strictly describes a faceted block with flat polished faces, it is used broadly for the pendant drops of many shapes that ornament glass lighting.
Cut glass drops came into fashion in the eighteenth century as English and Irish glasshouses perfected lead crystal, whose high refractive index produces brilliant flashes of rainbow colour. Common forms include long spear or icicle prisms, pear drops, almond or pendeloque drops, buttons, stars and chains of linked beads, often fixed with brass or silvered pins. Victorian mantel lustres and girandoles are hung with long faceted prisms that chime softly when moved. Coloured prisms in amethyst, amber and ruby glass were also made. When restoring a chandelier, matching replacement drops in size, colour and cutting style is important, since modern machine-cut or moulded glass looks noticeably different. Collectors check for chips, cloudiness and later replacements, and clean prisms gently by hand rather than in a dishwasher to protect the cut edges.
