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.
This word is spelt in many different ways.
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.
The modern value of ultramarine is about equal to its weight in gold. Sir Peter Lely, in the time of Charles II., paid £4. 10s. an ounce for it.
The Prior in question was the Superior of the Convent of the Frati Gesuati in Florence.