[262] In Cennino's time, the early part of the fourteenth century, in Europe, sugar was sold by the ounce as a costly drug. Apothecaries, not grocers, dealt in it. In Persia, Syria and some other Moslem countries cane sugar was made and used in comparatively large quantities throughout the mediaeval period; but in Europe it did not come into use as an article of food till the 16th century, and even then it was very expensive. [263] The date of this receipt is about 1410; it is quoted in Jehan de Begue's manuscript published by Mrs Merrifield, Vol. I. pp. 9, 95, and 154; see also Theophilus, I. 31, who speaks of burnishing fluid gold laid on a mordant of red lead and cinnabar. [264] See Theophilus, I. 33 and 34; he recommends white of egg as a medium for ceruse, minium and carmine, and for most other pigments, ordinary vellum _size_. Jehan le Begue's manuscript gives the same advice as to the use of white of egg, but advises the use of gum Arabic with other pigments; see § 197. [265] The British Museum possesses an interesting manuscript on pigments, entitled _De coloribus Illuminatorum_ (Sloane manuscripts, 1754); see also Eraclius, _De artibus Romanorum_, published by Raspe, London, 1783 and 1801; and the twelfth century _Mappae Clavicula_ printed in _Archæologia_, Vol. XXXII. pp. 183 to 244. The first book of Theophilus, _Diversarum artium schedula_, written in the eleventh century, contains much interesting matter on this subject; see also the works mentioned above at page 230. [266] _The Journal of the Society of Arts_, Dec. 25, 1891, and Jan. 8 and 15, 1892, has a valuable series of papers on "The pigments and vehicles of the Old Masters" by Mr A. P. Laurie, who throws new light on the treatises edited by Mrs Merrifield with the help of his own chemical investigations. [267] This word is spelt in many different ways. [268] In mediaeval times this was done by first embedding the powdered stone in a lump of wax and resin, from which the blue particles were laboriously extracted by long-continued kneading and washing. The theory of this apparently was that the wax held the colourless particles and allowed the blue to be washed out; see Mrs Merrifield, _Treatises on Painting_, Vol. I. pp. 49, and 97 to 111. [269] The modern value of ultramarine is about equal to its weight in gold. Sir Peter Lely, in the time of Charles II., paid £4. 10_s._ an ounce for it. [270] The Prior in question was the Superior of the Convent of the Frati Gesuati in Florence.