Naples Yellow

Synonyms:

Naples Yellow, Jaune de Naples, Jaune d'Antimoine, Neapelgelb, Giallo di Napoli

Under this name three different substances are included. The pigment generally sold in England as 'Naples yellow' is an excellent imitation made by mixing cadmium yellow or deep cadmium with a white, preferably a zinc white. But a true Naples yellow, which is a basic lead antimoniate, is still procurable from some artists' colourmen. This preparation is sometimes made by heating together for two hours a mixture of 1 part tartar emetic, 2 parts nitrate of lead, and 5 parts common salt, all the ingredients being of the purest quality, and the heat not exceeding that at which common salt fuses. A more recent process, in which zinc oxide is introduced among the materials which are heated together, yields a paler but excellent product. A bright pale variety of yellow ochre seems to have formerly gone under the name of Naples yellow.

This antimonial yellow has been known from very early times as an enamel colour. It has been found upon Babylonian bricks at least 2,500 years old. Persian pottery as early as the thirteenth century of our era is occasionally decorated with antimonial yellow.

In oil the genuine and the imitative Naples yellows are quite permanent, so far as light is concerned, but the genuine kind is liable to be darkened, like other lead compounds, by air containing sulphuretted hydrogen. In water-colour painting genuine Naples yellow is quite inadmissible, for it blackens rapidly, but irregularly, in the presence of mere traces of sulphur compounds. This blackening, like that of lead white under similar conditions, is much more marked in darkness than in light.

Naples yellow, in contact with metallic iron, tin, pewter, zinc, and several other metals, is discoloured and blackened. An ivory instead of a steel spatula, or palette knife, should be used with this pigment. The darkening in question is due in part to attrition, owing to the extreme hardness of the particles of the lead antimoniate, however finely the material may have been ground, and partly to the reducing effect of the above-named metals upon this antimoniate. Iron in the form of its oxide or hydrate (as in light red or yellow ochre), or in complex combinations (such as Prussian blue), does not exert any effect upon Naples yellow. A statement to the contrary effect has crept into a large number of technical manuals, but I have been unable to discover the slightest experimental evidence in favour of such a view. Naples yellow, however, is injured by and does injure some of the organic pigments, such as the cochineal reds and the numerous yellow lakes. But as Naples yellow cannot be used as a water colour, and as the above-named organic pigments ought to be entirely excluded from the palettes of all artists, the action in question is of little importance. Naples yellow acts upon indigo also.

Indigo, however, is a pigment, to which a very high degree of permanence cannot be assigned; there is, moreover, no reason why it should be associated with Naples yellow, as other yellow pigments may be safely used to modify its hue.

Another pigment also is sold as jaune d'antimoine. It is a mixture of the oxychlorides of bismuth and lead with lead antimoniate. When carefully prepared it yields a rich paint of good body, but its use cannot be recommended to artists.