Colored cements

Composite Gemstones. Many types of composite or assembled gemstones have been made (1). Some are shown in Figure 3. In the United States a doublet has two pieces combined using a colodess cement. If three pieces are used, or if two pieces are assembled using a colored cement, the gemstone is a triplet. The use of composite stones has declined rapidly with the rise of inexpensive synthetics. Frequendy seen are opal doublets, where precious opal is backed by a black material. In opal triplets a thin sHce of precious opal is cemented between a black backing and a clear cover, usually of quartz. Additionally, insects and even fish have been inserted into amber. 

About 60% of the natural iron oxide pigments is used to color cement and other building materials (qv). About 30% is consumed in the production of paints. For coloring plastics and mbber, synthetic iron oxide pigments are preferred. The main advantage of the natural iron oxide pigments, as compared to the synthetic ones, is cost. However, the quaHty is inferior, and in most cases, they are consumed in close proximity to the mines. As colorants, the natural iron oxides are about 50% weaker than synthetically produced iron oxides. 

Iron Oxide Yellows. From a chemical point of view, synthetic iron oxide yellows, also known as iron gelbs, are based on the iron(III) oxide—hydroxide, a-FeO(OH), known as goethite. Color varies from light yellows to dark buffs and is primarily determined by particle size, which is usually between 0.1 and 0.8 p.m. Because of their resistance to alkahes, these are used by the building industry to color cement. Thermally, iron oxide yellows are stable up to 177°C above this temperature they dehydrate to iron(III) oxide ... 

Specialty cements. For special architectural appHcations, white Pordand cement with a very low iron oxide content can be produced. Colored cements are usually prepared by intergrinding 5—10% of pigment with white cement. 

Building Materials. For standards, see Table 1 ( Coloration of building materials ). The following tests are prescribed for assessing the suitability of a pigment for coloring cement and lime-bonded building materials ... 

Natural iron oxide pigments are mostly used as inexpensive marine coatings or in coatings with a glue, oil, or lime base. They are also employed to color cement, artificial stone, and wallpaper. Ocher and sienna pigments are used in the production of crayons, drawing pastels, and chalks [3.5]. 

See also, in this regard, the remarks of a company dealing in colored cements and concretes Davis Colors, 3700 East Olympics Blvd., Los Angeles, CA 90023, www.coloredconcrete.com/davis/Tech/03470.html. 

Color Cement gray Pearl white Pure white Vehicle white... 

The colored cements can be produced from the white clinker. The technology consists in mixing white cement with mineral dyes, most often the metal oxides, added from 1 to 3 % by mass. There are some reports deahng with alternative colored cements technology, consisting on the production of colored chnkers [37]. 

Colored cements are manufactured so that concrete surfaces of a desired color can be produced. Cements of this type are used mainly for decorative purposes. 

A colored cement may also be produced by blending an ordinary or white cement with appropriate amoimts—up to 10%—of a suitable pigment. The pigment ... 

In the production of colored cements based on Portland cement it is also possible to... 

Table 24.1 lists a range of pigments that may be used in combination with white or ordinary Portland cement in the production of colored cements. Even though Portland cement is the binder most widely used for this pttrpose other types of cement may also be employed, such as calcirrm alrrminate cement. 

A white cement has also been produced by jointly grinding an electric arc furnace slag with gypsum. Such a binder may also be combined with srritable pigments to produce colored cements, but these are only very rarely used. 

Kholoshin, E.P., and Vavrenynk, S.V. (1992) Resource-saving colored cement mineral composition, in Proceedings 9thICCC, New Delhi, Vol. 3, pp. 444-448. 

Colored cement n. A cement to which color pigment has been added. 

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