Detail in other colours, Including white or red, were applied at this point. The relief line was probably drawn with a bristle brush or a hair, dipped in thick paint. (The suggestion that a hollow needle could account for such features seems somewhat unlikely.) The application of relief outlines was necessary, as the rather liquid glossy clay would otherwise have turned out too dull. After the technique's initial phase of development, both alternatives were used, so as to differentiate gradations and details more clearly. The space between figures was filled with a glossy grey clay slip. Then, the vases underwent triple-phase firing, during which the glossy clay reached its characteristic black or black-brown colour through reduction, the reddish color by a final re-oxidation. Since this final oxidizing phase was fired using lower temperatures, the glazed parts of the vase did not re-oxidize from black to red: their finer surface was melted (sintered) in the reducing phase, and now protected from oxygen.