It is not safe to take the older date-marks on porcelain at their face value. The Chinese with their proverbial veneration for antiquity habitually placed the date-marks of the classical reigns on their porcelain whether decorated in the style of the period mentioned or not. Already in the sixteenth century the Hsüan Tê and Ch'êng Hua marks were used in this way, and in the K'ang Hsi period the names of these two classic reigns were used more frequently than that of the K'ang Hsi period itself. In fact the Hsüan Tê and Ch'êng Hua are on the whole the most familiar marks of all, though the actual wares of these two periods are among the rarest. The date-marks of the other Ming Emperors are less frequently plagiarised, except upon the deliberate imitations of the wares of the time, such as those made at the Imperial factory in the Yung Chêng period, which we may be sure were carefully marked with the appropriate _nien hao_. Moreover, the Japanese, who have expended much ingenuity on reproducing Ming wares, have made free with Ming date-marks, especially those of Chia Ching and Wan Li. In the year 1677 the potters at Ching-tê Chên were forbidden by an order of the district prefect[448] to inscribe the period-name of the Emperor or any sacred writing on their porcelain, lest the names should be profaned in the breaking of the ware. It is certain that this prohibition was not effective for long; but probably the current date-mark was suppressed for a time at least, and it is quite likely that we should trace to this interval the custom of putting symbols or conventional marks inside the double ring which was usually occupied by the _nien hao_, a common practice in the K'ang Hsi period. In many cases, too, the rings were left empty; but it is a mistake to regard this as an infallible sign of K'ang Hsi manufacture, for it is a thing which might happen at any time through negligence, the rings being made by one person and the marks written by another. There are, besides, well authenticated instances of the empty double ring on Wan Li porcelain,[449] and on post K'ang Hsi wares. It was, however, such a frequent occurrence on the K'ang Hsi wares that the modern imitators make a common practice of leaving the rings blank on their copies of the K'ang Hsi blue and white. It is not clear whether the prefect's prohibition applied to the names of Ming emperors, but probably it did not, as it is unlikely that the adherents of the reigning dynasty would be sensitive about the titles of the house which they had exterminated. In any case, Ming marks, especially those of the fifteenth century, are very common on the K'ang Hsi porcelain, and the K'ang Hsi mark itself is comparatively rare except on the specimens which must belong to the later years of the reign.