Both in classical and mediaeval times it was usual for the patron who had ordered a picture to supply the necessary _ultramarine_ to the artist, who was only expected to provide the less costly pigments in return for the sum for which he had contracted to execute the work. _Method of theft._ Pliny (_Hist. Nat._ XXXIII. 120) tells a story of a trick played by a painter on his employer, who suspiciously watched the artist to see that he did not abstract any of the precious _ultramarine_ which had been doled out to him. At frequent intervals the painter washed his brush, dipped in the ultramarine, in a vessel of water; the heavy pigment sank to the bottom, and at the end of the day the artist poured off the water and secured the mass of powdered ultramarine at the bottom. It is interesting to note that Vasari, in his _life of Perugino_, tells precisely this story about Pietro, who was annoyed at the suspicions expressed by a certain Prior for whom he was painting a fresco[270]. The Prior was in despair at the enormous amount of pigment that the thirsty wall sucked in, and he was agreeably surprised when, at the conclusion of the work, Perugino returned to him a large quantity of _ultramarine_, as a lesson that he should not suspect a gentleman of being a thief. _Ultramarine scraped off._ The library of Corpus Christi College, Cambridge, possesses a manuscript which affords a curious proof of the great value of ultramarine to the mediaeval illuminator. This is a magnificent copy of the _Vulgate_ by a German scribe of the twelfth century, copiously illustrated with miniature pictures, many of which had backgrounds, either partially or wholly, covered with ultramarine. All through the book the ultramarine has in mediaeval times been very carefully and completely scraped off, no doubt for use in another manuscript. This theft has been accomplished with such skill that wonderfully little injury has been done to the beautiful illuminations, except, of course, the loss of splendour caused by the abstraction of the ultramarine. _Impasto._ In illuminated manuscripts _ultramarine_ is very freely used. It is specially noticeable for the thick body (_impasto_) in which it is applied, so as very often to stand out in visible relief. The reason of this is that this, and some other blue pigments, lose much of their depth of colour if they are ground into very fine powder. Hence both the ultramarine and _smalto_ blues are always applied in comparatively coarse grained powder; and this of course necessitates the application of a thick body of colour. _Ancient cyanus._