NAPLES YELLOW

Principally lead antimoniate, one of the colors already known to the old masters, that is said to have been found on the tiles of Babylon. It is very heavy and dense, and therefor of exceptional covering power; moreover as a lead color it is a good dryer, but poisonous as all leads are. Manufacturers distinguish between Naples yellow and dark Naples yellow; both are very permanent. The reddish Naples yellow however, is an impermanent mixture recolored with coal-tar dyes, chrome red, minium, or similar pigments, which is quite superfluous, but strangely favored by artists. In oil, tempera and even fresco, excellent use can be made of Naples yellow as it is compatible with all other colors. It is a much more compact compound of lead than is lead white, requiring only 15% oil, and it is totally unaffected by light. It seldom cracks, and in varnished tempera is invaluable because of its covering power. One claim on record is that it should never come into contact with a steel spatula as it turns grayish green, though this has never been proven to be the case. More likely the alleged discoloration is via an optical process when a thin layer lies over a dark background at which point it would appear this way. Also, that Naples yellow cannot be mixed with iron colors such as ochre is also erroneous. Discoloration has however been proven in tempera colors from the tube, where the metal of the tube was attacked by disinfectants contained in the tempera medium, which creates a dirty gray. Naples yellow needs little grinding; only a brief working with the spatula, and if too finely ground becomes heavier and earthy in texture, therefore best when made by hand, and not previously manufactured.

NATURAL & ARTIFICIAL BLUE COPPER PIGMENTS

Natural, coming under the title of: Mountain blue, Bremen blue, blue verditer, cendres blues, all of which are impermanent, highly poisonous and incompatible with many other colors including lead white and vermilion. Combined with sulphur colors such as cadmiums, all copper colors turn black. Though coppers were used by necessity in old paintings, they were isolated by layers of varnish and applied pure with egg tempera. In medieval times, the artificial copper blues were the answer for use in woodwork, sky blue ceilings etc., where the pigment couldn't cost more than the building; the poorer market could not supply the artist with azurite or ultramarine, thus these colors were probably more significant than all the rest. IN all of Cennino's accounts he never mentions these pigments at all. A standard of judgment on permanence also was not developed until later on, and pounds of copper blue were used to each ounce of ultramarine, and they were as mentioned, quite impermanent. There were also copper blues which depended upon the property of copper and ammonia to combine, in order to make the color required. A solution of copper sulphate, weak enough to look pale greenish blue, turns to a very dark blue if spirits of ammonia are added. The cuprammonium salt is formed which is dark blue; however, it is again, not durable, as the ammonia evaporates when not used quickly enough, leaving nothing but copper sulphate. With lime, it stabilizes instead, making it more durable for fresco. The many variations were all designed to produce cheap blues from common materials for everyday purposes. The weakness of these blues however, is their tendency to revert to green through loss of ammonia content, explaining the patches of bright green which appear in the blues of medieval wall paintings. One conspicuous example being in the values of the upper church of San Francisco at Assisi, which as of this entry, probably sustained damage in the recent earthquake there. This color change is usually attributed to a change of azurite into malachite, but it is more likely the result of the employment of a cuprammonium-lime blue.

NEW BLUE

Another name for artificial ultramarine blue.