Potash glasses

Lead oxide is a glass modifier that yields a very special type of glass known by a variety of names, including lead glass, flint glass, lead crystal, and 

As early as Roman times, it was found that the green coloration due to iron impurities could be offset by adding to the glass, while still in the molten 

most of the color in glass is produced by metallic ions derived from minerals, usually in relatively small amounts within the glass structure. Already in antiquity there was awareness of the effects of some other metals on the color of glass. It was known then, for example, that even relatively small amoxmts of specific metals, included as minerals in the components of a glass melt, could produce colored glass particular metalliferous minerals were therefore added to glass melts so as to produce special and 

Glass color Metal Ionic form environment 

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Medium 20,000-50,000 4 Acrylic resins, plastics, PVC, ammonium chloride, DMT, copper compounds, lead Ferroalloys, fluorspar, nickel Iron, potash, glass-making mixtures... 

Eali-glas, n. potash glass, -glimmer, m. potash mica, muscovite. kalUuLltig, a. containing potash. 

A reaction between sodium from the glass and atmospheric water and carbon dioxide can lead to the formation of sodium carbonate, which crystallizes in fine needles. A potash glass forms potassium carbonate, which is too deliquescent to crystallize out. A lead glass can react with hydrogen sulphide, and to a smaller extent with carbon dioxide, sulphur dioxide, and acid vapoiurs. 

A tube of thick-walled soft glass, about 50 cms. long, 12—13 mms. inside diameter, and walls 2—3 mms. thick. Tubes of hard potash glass with walls 2 mms. thick may also be used. The tube is carefully sealed at one end, in the manner described on p. 41, after which it is thoroughly washed and dried. 

Potassium Silicate, Soluble potash glass soluble... 

It is interesting that descriptions of the manufacture of smalt always cite potash as a flux. Potash glasses are less stable than soda glasses and this has affected the stability of the pigment, as noted above. It is unusual in glassmaking areas such as Venice and Eg)rpt, for example, that sodium was not used as a flux, being abundant from seaweed and other natural sources such as at Wadi Natrun. Further research is recpured in this area. 

As a coloring oxide in lead potash glasses, manganese produces an amethyst color, while in soda glass a reddish-violet is produced. 

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