The colouration of silicate glasses by tellurium is obtained by melting in reducingconditions 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

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... 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.