Many of the surfaces of the Alhambra are covered in ornamental plasterwork. The plaster is made of alabaster, gypsum or plaster of Paris. This type of carving in plaster is called yeseria. A slab of plaster was cut out in a studio or applied to the wall in situ. A design was marked on then surface then it was carved out using wooden or metal implements. Sometimes the plaster was painted or given a glaze to protect it from the elements. Retardants such as salts, glue or calcium carbonate were added to slow the setting and permit carving while panels were still damp.