Preparation and study of superficially coloured lead glass

Superficially coloured lead crystal glass was obtained by ion-exchange with silver. Both red and yellow ruby colouring were achieved by the presence of small silver particles (colloids) dispersed into the ion-exchanged glass surface. Direct silver ion-exchange of the glass yielded yellow colouring (optical absorption around 410 nm). Silver ion-exchange of lead glass previously doped with a reducing agent (i.e., arsenic oxide) yielded red colouring, (optical absorption around 600 nm), which indicated special arrangement for silver colloids in the exchanged layer. Parameters that influenced the ion-exchange process, such as temperature, exchange time, dopant percentage and composition of molten salts bath (where the ion-exchange took place), were examined in order to select the best conditions to obtain colours with decorative interest. Optical absorption spectroscopy and scanning electron microscopy were used to determine colour coordinates and silver diffusion profiles, respectively. Direct observation of the silver colloids were performed by means of transmission electron microscopy. Finally, once the optimum process parameters were tested, an intense red ruby colouring (more than 98% colour purity) was reached. Industrial application of this process arises positively, since some handicaps from traditional bulk colouring could be avoided. C 2005 Springer Science + Business Media, Inc.