Zirconia is most commonly used in a stabilised form. As an unstabilised material, it is mainly used as an additive, a coating material, or an abrasive in powder form. Zirconia is added to glass and to glazes to increase their resistance to alkaline solutions and also to glazes in higher concentrations as an opacifier. Additions of Zirconia to alumina increase the toughness, strength and wear resistance of the material. Plasma sprayed Zirconia coatings show good thermal insulating properties at the temperatures encountered in jet engine combustion chambers.