Gypsum (sulphate of lime or plaster of Paris) steeped in a solution of alum (double sulphate of aluminium and potassium) then subjected to intense heat, ground to a powder, and sifted. Invented around 1840, and also called Martin's or Parian cement, it was exceptionally hard when dry, took a high polish, and could also be coloured. Easily cleaned, it was often used for skirtings, dados, mouldings, and even floor-surfaces. It was combined with marble for parts of the interior of Butterfield's Church of All Saints, Margaret Street, London (1848–59).
Architects' Journal, cxci/25 (20 June 1990), 36–55;W. Papworth (1852)