The synthesis of a black Fe2O3-Cr2O3 pigment has been studied to better understand the synthesis mechanism. A mechanism is proposed according to which, under the tested operating conditions, one of the starting constituents (Cr2O3) is transferred, largely in a gas phase (after subliming), to the particle surface of the other constituent (Fe2O3), at which it is deposited or chemisorbed, forming a layer from which it diffuses inward into the Fe2O3 particles. The process stops when the composition of the resulting solid solution has became uniform.