plaster: a mixture of lime or gypsum with sand and water; hardens into a smooth solid; used to cover walls and ceilings
mixture: (chemistry) a substance consisting of two or more substances mixed together (not in fixed proportions and not with chemical bonding)
forbidden fruit: originally an apple from the tree of knowledge of good and evil in the Garden of Eden; it is now used to refer to anything that is tempting but dangerous (as sexuality)