This page has been proofread, but needs to be validated.



the five sets of opposite hues described in Chapter III., paragraphs 61–63:—

Color Pairs. Pigments Used. Chemical Nature.
Red and Venetian red. Calcined native earth.
Blue-green. Viridian and Cobalt. Chromium sesquioxide.
Yellow Raw Sienna. Native earth.
Purple-blue. Ultramarine. Artificial product.
Green Emerald green. Arsenate of copper.
Red-purple. Purple madder. Extract of the madder plant.
Blue Cobalt. Oxide of cobalt with alumina.
Yellow-red. Orange cadmium. Sulphide of cadmium.
Purple Madder and cobalt. See each pigment above.
Green-yellow. Emerald green and Sienna. See each pigment above.

(105) These paints have various degrees of hue, value, and chroma, but can be tempered by additions of the neutrals, zinc An image should appear at this position in the text. white and ivory black, until each is brought to a middle value and tested on the value scale. After each pair has been thus balanced, they are painted in their appropriate spaces on the globe, forming an equator of balanced hues.

(106) The method of proving this balance has already been suggested in Chapter IV., paragraph 93. It consists of an ingenious implement devised by Clerk-Maxwell, which gives us a result of mixing colors without the chemical risks of letting them come in contact, and also measures accurately the quantity of each which is used (Fig. 17).

(107) This is called a Maxwell disc, and is nothing more than