To obtain the best colour from the copper oxide in this glaze it was necessary to regulate the firing to a nicety, the margin between success and failure being exceedingly small. Naturally, too, the results varied widely in quality and tone; but the permanent characteristics of the K’ang Hsi _sang de bœuf_ are (1) a brilliant red varying in depth and sometimes entirely lost in places,[268] but always red and without any of the grey or grey blue streaks which emerge on the _flambé_ red and the modern imitations of the _sang de bœuf_; (2) the faint crackle of the glaze; (3) the stopping of the glaze at the foot rim. The colour of the glaze under the base and in the interior of vases varied from green or buff crackle to plain white. The secret of this glaze, which Père d’Entrecolles tells us was carefully guarded, seems to have been lost altogether about the end of the K’ang Hsi period. Later attempts to obtain the same effects, though often successful in producing large areas of brilliant red, are usually more or less streaked with alien tints such as grey or bluish grey, and are almost invariably marred by the inability of the later potters to control the flow of the glaze which overruns the foot rim and consequently has to be ground off. But it is highly probable that the modern potter will yet surmount these difficulties, and I have actually seen a large bowl of modern make in which the ox-blood red was successfully achieved on the exterior (the interior was relatively poor), and the flow of the glaze had been stopped along the foot rim except in one or two small places where the grinding was cleverly masked. So that it behoves the collector to be on his guard.