An aristotype is a high-symmetry structure type that can be viewed as an idealized version of a lower-symmetry structure. It was introduced by Helen Megaw in relation to perovskites, where it is still mostly used. The cubic perovskite structure (which is adopted at most by half a dozen compounds) is regarded as the aristotype for the vast array of other lower-symmetry perovskites. The lower-symmetry structure is called hettotype . After Buerger, aristotypes are also known as basic structures and hettotypes as derivative structures . Originally, an aristotype is a printing-out process using paper coated with silver chloride in gelatin; now, any such process using silver salts in either collodion or gelatin; also, a print so made.