Coloring Glass and Glazes

We can use a similar argument to show how the addition of rare earth (RE) elements, with incomplete f shells, also causes color. Table 32.3 shows the colors produced 

TABLE 32.3 Optical Absorption of Rare Earth Ions in Oxide Glasses  

Uses for colored glass include not only the obvious stained glass windows and Tiffany lampshades but also the glazes used to seal and decorate cups and pots. Adding Pb to make X-ray-absorbing glass is essentially the same process/motivation the intent is to absorb the X-rays. 

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Humans have been using compounds of cobalt since at least 1400 bce. The compounds were used to color glass and glazes blue. In 1735, Swedish chemist Georg Brandt (1694—1768) analyzed a dark blue pigment found in copper ore. Brandt demonstrated that the pigment contained a new element, later named cobalt. 

Erbium has a limited use. It is, however, possible to exploit the fact that, like many lanthanides, the element has specific light absorption characteristics. Erbium oxide, itself rose pink, colors glass and glazing. This glass absorbs infrared radiation. 

Lead antimonate [13510-89-9] (Naples yellow), Pb2(Sb0 2> mol wt 993.07, d = 6.58g/cm, is an orange-yeUow powder that is insoluble in water and dilute acids, but very slightly soluble in hydrochloric acid. Lead antimonates are modifiers for ferroelectric lead titanates, pigments in oil-base paints, and colorants for glasses and glazes (see Colorants for ceramics). They are made by the reaction of lead nitrate and potassium antimonate solutions, followed by concentration and crystallization. 

This oxide is used in making blue and green colored glass and in glazes for pottery, but in recent years the preparation of superconducting materials such as YBa2Cu307 has become a serious interest. Other materials containing mixed oxides have also been produced. 

Cobalt ores are often found in association with copper(II) sulfide. Cobalt is a silver-gray metal and is used mainly for alloying with iron. Alnico steel, an alloy of iron, nickel, cobalt, and aluminum, is used to make permanent magnets like those used in loudspeakers. Cobalt steels are hard enough to be used as surgical steels, drill bits, and lathe tools. Cobalt(II) oxide is a blue salt used to color glass and ceramic glazes. We need cobalt in our diet, for it is a component of vitamin B12. 

This oxide is used in making blue- and green-colored glass and in glazes for pottery. 

Before 1942 uranium was said to have no important uses—it was used mainly to gi5 e a greenish-yellow color to glass and glazes. In 1942, hotvever, exactly one hundred years after the metal was first isolated, uranium became one of the most important of all elements. It was discovered in that year that uranium could be made a source of nuclear energy, liberated in tremendous quantity at the will of man. 

Even before alchemy became a subject of study, many chemical reactions were used and the products applied to daily life. For example, the first metals used were probably gold and copper, which can be found in the metallic state. Copper can also be readily formed by the reduction of malachite—basic copper carbonate, Cu2(C03)(0H)2—in charcoal fires. Silver, tin, antimony, and lead were also known as early as 3000 BC. Iron appeared in classical Greece and in other areas around the Mediterranean Sea by 1500 BC. At about the same time, colored glasses and ceramic glazes, largely composed of silicon dioxide (Si02, the major component of sand) and other metallic oxides, which had been melted and allowed to cool to amorphous solids, were introduced. 

Cobalt dyes have been used for centuries. Craftsmen used materials from the earth to color glass, pottery, glazes, and other materials. Cobalt minerals were especially prized for their rich blue color. 

Co(II) oxide, CoO(s), is a deep blue salt used to color glass and ceramic glazes. 

Other important end products include catalysts, pigments, cobalt oxides for glass and glaze coloring and cobalt salts as fertilizers. 

Elemental chemical analysis provides information regarding the formulation and coloring oxides of glazes and glasses. Energy-dispersive x-ray fluorescence spectrometry is very convenient. However, using this technique the analysis for elements of low atomic numbers is quite difficult, even when vacuum or helium paths are used. The electron-beam microprobe has proven to be an extremely useful tool for this purpose (106). Emission spectroscopy and activation analysis have also been appHed successfully in these studies (101). 

Cadmium acetate is a colorant for glass and textiles, a glaze for ceramics where it produces iridescent effects, a starting material for preparation of the cadmium haUdes, and is an alternative to the cyanide bath for cadmium electroplating. In 1991, cadmium acetate dihydrate sold for 59.50/kg in 2 kg lots of reagent-grade material. 

The pure compound is used in glazes and enamels as an opacifying agent. It also is used to make colored glass, imparting yellow color to the glass. The crude form is used in flaming arc lamps. Another application of this compound is in the preparation of several other cerium salts. 

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