Chrome yellows are lead chromates, produced by mixing dilute solutions of lead acetate or nitrate and potash bichromate; this makes a medium tint known as "middle chrome." The addition of lead sulphate makes this paler, when it is known as "lemon chrome," whereas the addition of caustic lime makes it "orange chrome" of a darker colour. The chromes mix well with oil and with white-lead either in oil or water; stand the sun well, but, like other lead salts, become dark in bad air. Chrome yellow is frequently adulterated with gypsum. "Naples yellow" is a salt of lead and antimony; is not so brilliant as chrome, but has the same characteristics. "King's yellow" is made from arsenic, and is therefore a dangerous pigment to use in internal work; is not durable, and injures several other colours when mixed with them. "Chinese yellow," "arsenic yellow," and "yellow orpiment" are other names for king's yellow. Yellow ochre is a natural clay, coloured by iron oxide, and found abundantly in many parts of England; is not very brilliant, but is well suited for distemper work, as it is not affected by light or air; does not lose its colour when mixed with lime, as some other pigments do. "Spruce ochre" is a variety of brownish-yellow colour. "Oxford ochre" is of a warm yellow colour and soft texture, absorbent of both oil and water. "Stone ochre" is found in the form of balls imbedded in the stone of the Cotswold hills; varies in tint from yellow to brown. "Raw sienna" is a clay, stained with oxides of iron and manganese, and of a dull yellow colour; is durable both in oil and water, and useful in all work, especially graining. "Yellow lake" is a pigment made from turmeric, alum, etc.; is not durable, and does not mix well with oil or metallic colours.