Glass - Back to the Future!

Presenting Author:
Georg Partzsch

article posted 06 April 2016

Georg Partzsch obtained his diploma in mineralogy from the Technical University Berlin (1992), followed by his doctoral degree from Free University Berlin in 1997. He continued his career at the University Heidelberg doing research work. In 2004 he changed to Swarovski for the development of colored glasses. His main functions today, as a senior glass engineer, are the development of colored glasses particularly gold ruby glasses and the stabilization of glass production processes.

Replacement of Lead in Gold Ruby Glass Made by Swarovski

Georg M. Partzsch* & Stefan Prowatke, D. Swarovski KG, Swarovskistr. 30, 6112 Wattens, Austria

In the last few decades the use of hazardous heavy metals came into disrepute because of environmental and health concerns. To avoid the use of such heavy metals Swarovski changed its glass production to lead and arsenic free compositions. We started some years ago with our standard crystal glass production and developed a new lead free crystal glass composition for all our different products.
Now the production of the coloured glass was also changed to a lead and arsenic free formula. More than 100 different colours were affected. A special challenge was the transformation of the gold ruby glass. Because the new lead free gold rubies have to be equal to the old ones in colour and quality.
Since its invention the red colored gold ruby glass has always been, because of its rareness and beauty, a very high rated treasure. Moreover, the production was very difficult so the gold ruby was surrounded with mystery. During the 19th century glassmakers learned that the production of gold ruby is facilitated by the use of lead crystal base glass. Some arsenic was also added not only for fining but also to raise the brilliance of the colour. It is well known that the colour caused by gold is due to gold nano particles (colloids). The colloids are formed during the tempering of the glass (striking) above Tg. The colloidal colour is determined by number and size of the colloids.
Swarovski is now able to produce gold ruby glass with the required characteristics using a new glass composition and substitution of lead and arsenic by tin and antimony. With an exact control of the whole production process we are able to determine number and size of the gold colloids and therefore the color of the glass. The different colors produced with one single melt are shown in dependence of time and temperature of the tempering (Time-Temperature-Color-Diagram, TTC-Diagram). Actually with our new glass composition colors due to gold colloids can be produced reaching from a pale yellowish rose over rose, red, violet, to blue. By the addition of rare earth elements even more colors such as orange can be produced.