A study of the Casing of Colourless Cobalt Blue Glass Part. I

JSGT 1928 V12 T057-T074

In 1924, an account was given by one of us at a meeting of the Society at Stourbridge of the properties of glasses containing lead oxide. At that same meeting, Mr John Northwood described the work involved in the reproduction of the Portland vase; and during the discussion which followed both papers the subject of the relationship between the thermal expansion of two glasses, one welded to or cased on the other, was referred to. It appeared to be a fairly general belief that the essential requirement for two glasses which are to be welded is that their coefficients of thermal expansion shall be as nearly as possible the same. Manufacturers of cased glasses have found from experience, however, that a coloured glass which has been coloured by the addition to the colourless base glass of a small amount of colouring matter cannot always be successfully welded to the base glass itself, and it is the usual practice, in order to obtain successful welding, to employ as coloured glass one which is relatively softer than the base glass. Hence the question has been raised by several practical workers as to whether or not the colouring agent brings about some marked modification of the thermal expansion as compared with the colourless glass.

W. E. S. Turner & Francis Winks