This section is from the book "Chromatography; Or, A Treatise On Colours And Pigments, And Of Their Powers In Painting", by George Field. Also available from Amazon: Chromatography, or A Treatise on Colours and Pigments, and of Their Powers in Painting.
Naples Yellow is a compound of the oxides of lead and antimony, antiently prepared at Naples under the name of Giallolini; it is supposed also to have been a native production of Vesuvius and other volcanoes, and is a pigment of deservedly considerable reputation. It is not so vivid a colour as either of the above, but is variously of a pleasing light, warm, golden yellow tint. Like all the preceding yellows it is opaque, and in this sense is of good body. It is not changed by the light of the Bun, and may be used safely in oil or varnish, under the same management as the whites of lead; but, like these latter pigments also, it is liable to change even to blackness by damp and impure air when used as a water-colour, or unprotected by oil or varnish.
Iron is also destructive of the colour of Naples yellow, on which account great care is requisite, in grinding and using it, not to touch it with the common steel palette-knife, but to compound its tints on the palette with a spatula of ivory or horn. For the same reason it may be liable to change in composition with the ochres, Prussian and Antwerp blues, and all other pigments of which iron is an ingredient or principal. Oils, varnishes, and, in some measure, strong mucilages, are preventive of chemical action, in the compounding of colours, by intervening and clothing the particles of pigments, and also preserve their colours; and hence, in some instances, heterogeneous and injudicious tints and mixtures have stood well, but are not to be relied on in practice. Used pure, or with white lead, its affinity with which gives permanency to their tints, Naples yellow is a valuable and proved colour in oil, in which also it works and dries well.
It may also be used in enamel painting, as it vitrifies without change, and in this state it was formerly employed under the name of Giallolini di fornace, and has been again introduced, under an erroneous conception that vitrification gives permanence to colours, when in truth it only increases the difficulty of levigation, and injures their texture for working. Naples yellow does not appear to have been generally employed by the early painters in oil.