THE INFLUENCE OF THE IRON CONCENTRATION AND THE FE2+ FE3+ REDOX RATIOON THE CRYSTALLIZATION OF BIOVERIT-II/

Transition metal ions do not solely influence the optical properties o f glasses but also their crystallisation behavior. In the case of iron in a mica glass ceramic, Fe3+ leads to smaller mica-aggregates and su ppresses the crystallisation of indialith. Tn glasses melted under red ucing conditions, Fe2+ is formed which is incorporated into the indial ith and leads to a preferred crystallisation of this phase. Tron does not act as a simple colouring additive but influences the whole nuclea tion and crystallisation process.