or Keen’s cement. Patented by J.D. Greenwood and R.W. Keen in 1838. It is a type of interior wall plaster obtained from gypsum. Gypsum is heated above 1708C to form anhydrous calcium sulphate. This was soaked in a solution of alum (potassium aluminium sulphate) to accelerate the set. The mixture was then reheated to 400-5008C and ground to form a plaster. Because Keene’s cement sets more slowly than gypsum plaster it is easier to use; it does however set more rapidly than lime and produces a hard, smooth finish which can be painted or wallpapered within a few hours of application. Ashurst (1983); Trench (2000). [J. Cassar, R. de Angelis]