Mineral Pigments (90157bf0-a3ff-400f-b90a-00bb94342425)

Mineral pigments give color, opacity, or body to paint, stucco, plaster, mortar, cement, linoleum, rubber, and similar materials. They must be finely divided, substantially insoluble, and generally inert for such uses. Inorganic pigments may be grouped somewhat arbitrarily as follows: A. Natural mineral pigments dug from the earth. 1. Those consisting mostly of iron oxides, such as hematite and limonite. 2. Those containing large amounts of clay or noncoloring matter, such as ocher, sienna, umber, and colored shales. 3. Those whose color is not due to iron oxide, such as Vandyke brown (including sap brown, an alkali extract of Vandyke brown), graphite, and terre verte. B. Synthetic pigments. 1. Those containing iron oxide as the essential coloring matter, such as "pure" reds, yellows, and blacks, and Venetian reds. 2. Those not containing iron oxide, but rather such compounds as lithopone, zinc white, titanium white, ultramarine, Prussian blue, and the like. Only groups A and B-1 are discussed here. All the pigments in those two categories, except Vandyke brown, sap brown, and some of the carbonaceous slates, contain, as their essential color constituents, one or more compounds of iron; namely, an oxide-limonite (2Fe2O3.H2O to Fe2O3.4H20), hematite (Fe2O3), or magnetite (Fe2O3.FeO). Man's first permanent coloring materials were earth pigments-the ochers, iron oxides, and various iron-stained clays. The caves occupied by prehistoric man and the arts of the ancient Chaldean, Egyptian, and Cretan civilizations bear mute witness to this and also testify to the beauty and permanence of earth colors. As the Roman era developed, earth pigments were pushed from their pre-eminent position by white lead and red lead and in the Middle Ages by zinc oxide. Today, of course, the number of acceptable pigments is very large and on a value basis the group of natural and synthetic earth pigments stands forth with $16,000,000 per year; it is surpassed by titanium, lead and zinc pigments. Of this sum,21 natural pigments supplied 31 pct of the tonnage and 16 pct of the value of the total finished pigment in 1957, the remainder representing the tonnage and value of sales of the synthetic iron oxide colors. The average value of finished natural pigments in 1958 was $80.62 per ton. The average value of manufactured pigments in the same year was $202 per ton. Of the 60,000 tons of manufactured colored pigments sold in 1958, the reds comprised 76 pct of the market and the yellows 20 pct. The reds furnished 68 pct of the value and the yellows 24 pct. Of the finished iron oxide pigments (natural and manufactured) sold in 1958, the reds dominated the market with 66 pct of the quantity and 63 pct of the value; yellows supplied 17 pct of the quantity and 20 pct of the value, and browns furnished 11 pct of the quantity and 10 pct of the value. The average value of the reds was approximately $152, and the average value of the yellows $190 per ton. The highest valued pigment in 1958, with almost 12 pct of the total tonnage and 21 pct of the value of the iron oxide pigment market, was manufactured red from calcined copperas valued at $286 per ton.