The present application discloses: (i) novel glass-ceramic materials containing a solid solution of b-quartz or of .beta.-spodumene as main crystalline phase(s); (ii) articles made from said novel glass-ceramic materials; (iii) lithium alumino-silicate glasses, precursors of such novel glass-ceramic materials; and (iv) methods for preparing the aforesaid novel glass-ceramic materials and the aforesaid articles made of said novel glass-ceramic materials. The present invention relates to the use of SnO.sub.2 (0.15 to 0.3% by weight) and CeO.sub.2 and/or MnO.sub.2 (0.7 to 1.5% by weight), as an agent for fining the glass-ceramic material glass precursor.