The Discoloration produced by Lead, Antimony, and Arsenic in Lampworked Glass Tubing

JSGT 1920 V04 T158-T161 (4 pages)

During the course of a long series of glass meltings for the production of tubing for lampworking purposes, we found that the addition of white arsenic or of antimony oxide to the batch always led to a glass which became discoloured on working in the blowpipe flame. The facts then ascertained seemed to us to be worthy of closer study; for, as we pointed out at the time, whilst most of the best samples of lampworking tubing previously made on the Continent were free from arsenic or antimony, occasionally arsenic was present, whilst in one noteworthy case as much as 3·45% of antimony oxide was contained in the finished glass. Arsenious oxide and antimony oxide are not the only oxides liable to cause discoloration in lampworked glass. Lead oxide, for example, may be a source of trouble. When the glass is known to be a lead glass, it can be worked satisfactorily in the oxidising part of the flame. The blackening of tubing, not ostensibly of lead glass, has been alleged to be due to the accidental addition of lead glass cullet to the batch, but the amount of such cullet necessary to produce the' effect has never been ascertained, nor has the amount of lead oxide. It seemed desirable, therefore, to obtain final proof of the detrimental effects of arsenious and antimony oxides, to ascertain what amounts were effective in causing discoloration, and to determine what proportion of lead oxide was necessary to cause blackening.

F. W. Hodkin & W. E. S. Turner