Cobalt is added to molten glass to produce a deep blue color, with only 0.5% needed for a striking effect. Iron or manganese can be added to tone down the color. Cobalt glass is used as an optical filter for flame tests and as a pigment for paints and ceramics.
Cobalt glass is the deep blue combination of glass and cobalt metal, with the blue tint resulting from cobalt inclusions. Very little cobalt is added to the molten glass to produce the color; a glass structure with 0.5 percent cobalt will give it a powerful blue color, with manganese and iron commonly added to tone down the color. In addition to a pleasant appearance, cobalt glass can be used as an optical filter for flame tests, because it filters out the contaminating colors expressed by iron and sodium. Enamel, or powdered cobalt glass, is used as a pigment for paints and ceramics.
When glass is made by heating sand and other carbon sources to very high temperatures, the heat causes the carbon to become a molten substance. Before the glass cools and solidifies, cobalt can be added to the mixture to give the glass a deep blue color. Cobalt is one of the strongest pigmenting metals, so only a very small amount is needed to achieve the blue tint. Most glass will only need 0.5 percent cobalt to produce striking color.
Cobalt is such a strong dye that it can easily create a powerful blue color, but some manufacturers may want a more subdued shade of blue. To achieve this, and to ensure that there is enough cobalt in the glass mix, iron or manganese is added to the glass. In addition to making the glass harder, this also mutes the cobalt blue.
While cobalt glass looks ornate and is a prized material for many collectors, it also has practical application for scientists performing flame tests. A flame test is a test in which a substance is placed over a flame and the change in the color of the flame determines which metals are in the substance. If there is no optical filter, sodium and iron contaminate the color of the flame, making it look too yellow. Using cobalt glass as an optical filter balances color and makes it easier for scientists to visualize metal ions.
Another function of this glass is as an enamel or cobalt glass that has been crushed into a powder. Glaze is used in pottery and paint to lend its powerful blue pigment to these mediums. This was often used in the past, but synthetic pigments are more used in contemporary times, because they are cheaper to make and reproduce the same color every time. Some hobbyists and professionals still use enamel, although it is more expensive.
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