Cookson Matthey Ceramics & Materials Limited

Harbans Kaur Mangat

Peter John Smith

Shaun Wingfield

Richard J Hall

Cobalt glass compositions for coatings

An on-glaze low expansion glass flux composition suitable for coating onto a glazed surface which is essentially free from lead and cadmium and comprises, in mole percent, SiO.sub.2 : 35 to 75%, Bi.sub.2 O.sub.3 : 4 to 12%, Al.sub.2 O.sub.3 : 2 to 12%, B.sub.2 O.sub.3 : 18 to 35%, at least one of Li.sub.2 O, Na.sub.2 O, K.sub.2 O : 0 to 12% (in total), and certain other optional ingredients with the provisos that BaO is not contained in an amount of more than 2 mole percent, the total amount of Bi.sub.2 O.sub.3 +B.sub.2 O.sub.3 +Li.sub.2 O,Na.sub.2 O and K.sub.2 O is in the range of from 25 to 45 mole percent, the total amount of Li.sub.2 O, Na.sub.2 O and K.sub.2 O is in the range of up to 10 percent by weight except when the only alkali metal oxide present is Li.sub.2 O, and the composition has a coefficient of thermal expansion in the range of from 4.0 to 7.0.times.10.sup.-6 /.degree.C. These glass flux compositions are of particular use in the preparation of enamel compositions for the decoration of low-expansion porcelain ware.

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Harbans Kaur Mangat