Poly crystalline and single‐crystalline α‐alumina were reacted with a eutectic CaO‐Al2O3 melt at 1530°C. A reaction zone develops in which a strongly textured CA6 layer, as well as a CA2 layer, forms, with a remaining layer of unreacted CaO‐AI2O3 melt. Silica, an impurity in the α‐alumina, is rejected by the advancing CA6 phase and accumulates as calcium alumino‐silicates in channels that assist in the reaction as fast transport paths. Reaction mechanisms and welding are briefly discussed.