1. R. J. Lumby and R. F. Coe, Proc. Brit. Ceram. Soc. 15 (1970) 91.
2. S. Wild, P. Grieveson, K. H. Jack and M. Latimer, Special Ceramics 5 (1972) 377.
3. I. Colquhoun, O. P. Thompson, W. I. Wilson, P. Grieveson and K. H. Jack, presented at the British Ceramic Society Convention 1972, in the press.
4. K. H. Jack and W. I. Wilson, Nature 238 No. 8 (1972) 28.
5. R. F. Horsley, R. J. Lumby, R. R. Wills, R. F. Coe private communication, J. Lucas Ltd, Monks path, Solihull.