of Ephesus, who practiced medicine around 100-140 AD. Other clays used in classical times The other types of clay that were famous in antiquity were as follows. Terra chia, Terra cymolia (Cimolean earth): these were both white earths and considered of great value. Samian earth: Pliny in c. 50 AD (Nat. Hist.) details two distinct varieties, colyrium - an eye salve, and aster, which was used as a soap as well as in medicines. Terra sigillata strigoniensis (Strigian earth, derived from Silesia) - this clay, yellow in colour, appears to have been famous later in medieval times. All the above seem to have been bentonitic clays. The earth which did not stain the hands was known as rubrica. Medieval times In medieval Persia, Avicenna (980-1037 CE), the 'Prince of Doctors', wrote about clay therapy in his numerous treatises. Ibn al-Baitar (1197–1248), a Muslim scholar born at Malaga, Spain, and author of a famous work on pharmacology, discusses eight kinds of medicinal earth. The eight kinds are: the terra sigillata, Egyptian earth, Samian earth, earth of Chios, Cimolean earth or pure clay (cimolite), soft earth, called al-hurr, green in color like verdigris, is smoked together with almond bark to serve as food when it will turn red and assume a good flavor; it is but rarely eaten without being smoked—also called 'Argentiera', earth of vines called ampelitis (Pliny XXXV, 56) or pharmakitis from Seleucia in Syria, Armenian earth (also known as the Armenian bole), salutary in cases of bubonic plague, being administered both externally and internally, earth of Nishapur. Renaissance period A French naturalist Pierre Belon (1517–1564) was interested in investigating the mystery of the Lemnian clay. In 1543, he visited Constantinople where, after making enquiries, he encountered 18 types of different products marketed as Lemnian Earth (he was concerned about possible counterfeits). He then made a special journey to Lemnos, where he continued his investigation, and tried to find the source of the clay. He discovered that it was extracted only once a year (on 6 August) under the supervision of Christian monks and Turkish officials. Preparation of clay Clay gathered from its original source deposit is refined and processed in various ways by manufacturers. This can include heating or baking the clay, since the raw clay tends to contain a variety of microorganisms. Too much processing, likewise, may reduce the clay's therapeutic potential. In particular, Mascolo et al. studied