The Platinum Metals in Glass

Platinum metals have long been used in the glass industry for crucibles and liners because of their high melting points and their chemical inertness to most molten glasses. Contamination of glass by platinum metals has not been reported except in one or two instances where the glasses had a high content of lead or barium. It is well known that heavy lead glasses are more susceptible to colouring by traces of impurity than other types of glass, and Hampton (I) and his co-workers found that glass of this type, even when made from very pure materials, became coloured when heated in platinum. He was able to produce a colourless specimen only by melting in a thoria crucible. Some optical glass manufacturers have also found a reddish colour in glass having a high lead or barium content after contact with a rhodium-platinum crucible; this coloration was probably due to traces of rhodium in the glass. Another instance of glass becoming coloured by platinum was reported in 1947 when Rindone, Marboe and Weyl (2) were working on the electrolytic oxidation and reduction of glasses containing various metal ions. Platinum electrodes were used and it was found that platinum ions from the anode tended to pass into solution in the glass. In borate glass the platinum ions were unstable and either reverted to metal, which was precipitated in the glass because of the low solubility of platinum, or, under certain conditions of temperature and viscosity, gave pink colloidal platinum producing a glass analogous to the familiar gold-ruby. Phosphate glasses were known to have a stabilising effect on silver ions in glass solution and they exhibited the same behaviour towards platinum, giving amber-coloured glass, the colour being similar to that of a solution of platinic chloride.