Study on the Silicate Glasses Coloured by Tellurium

The colouration of silicate glasses by tellurium is obtained by melting in reducing conditions and their colours are various corresponding to the degree of reduction. They are yellowish green, pink, purple pink, and red purple and are shown in the C. I. E. chromaticity diagram. These colouration are deepend by reheating. The purple pink and red purple can be obtatied with the potassium containing glass. Sodium containing glass is only able to become orange pink to pink.The authors calculate the index of the reducing capacity for various reducing agents and then calculate the ratio of reducing agents to unit weight of tellurium for the reduction of tellurium to alkalitelluride in glass. Using these values the authors investigate the influence of glass composition on the effectiveness of various reducing agents. The necessary amount of reducing agent to produce red colouration is affected by the glass components and must be increased when glass contains such component as calcium oxide, zince oxide, barium oxide, lead oxide, especially boric oxide and arsenic oxide. With the exception of aluminium, many other reducing agents tested, i.e. zinc and tartaric salts, etc., are not effective for the multicomponent glasses.The authors allude to the result of L. Springer, Sprechsaal, 88, 192-193 (1955), which conclude that the silicate glasses are not coloured red by tellurium. From his data the authors assume that his failure to get red colouration with tellurium is due to the wrong selection of the sort and amount of reducing agent for multi-component glass.From the practical point of view the authors conclude that it is able to obtain the tellurium pink or red silicate glasses by selecting the glass composition and the reducing agent suitable for the formation of alkali telluride and polytelluride in glass melt.