Fundamental Studies of the Melting Processes of Glasses Containing Lead Oxide. III. The Effect on the Melting Rate and Devitrification Temperature of a Potash-Lead Oxide-Silica Glass of the Substitution of Lead Oxide by Lime or Barium Oxide, Including an Examination of Some Commercial Glass Compositions.
JSGT 1941 V25 T241-T248
The relative melting rates and the devitrification temperatures have been determined of two series of glasses of parent composition 54% SiO2, 34 PbO, 12 K2O in which PbO was progressively replaced by 0-6% BaO, and by 0-6% CaO. Both these oxides resulted in easier melting and refining, the devitrification temperatures being reduced from 1020° to 920° for the 6% BaO glass, and to 915° for the 6% CaO glass. A comparison was made with nine commercial compositions known to be in use for the manufacture of domestic ware, the quicker melting rate of the majority of these glasses being due to the relatively high alkali contents, ranging from 12.56 to 18.2%. Based on one of these compositions, the melting rates and devitrification temperatures were determined of a series of glasses of composition 64% SiO2, 20 PbO, 1.5 BaO, 1·5 CaO, (12 - x)K2O and xNa2O. Of this series, the glass containing 4% K2O and 8% Na2O appeared to be of greatest promise. It gave an excellent colourless glass, the cutting qualities of which compared favourably with those of the lead crystal glass commonly used in Great Britain, was rather more easily melted than that glass, and should be a durable glass.
Eric Preston, Ph.D., D.Sc., F.I.C., F.Inst.P., and Professor W. E. S. Turner
