Another development of the _yao pien_ at this time is the use of a separate “transmutation” glaze which could be added in large or small patches over another glaze, and which assumed, when fired, the usual _flambé_ appearance. When judiciously applied the effect of this superadded _flambé_ was very effective, but it is often used in a capricious fashion, with results rather curious than beautiful. There are, for instance, examples of blue and white vases being wholly or partially coated with _flambé_, which have little interest except as evidence that the potters could now produce the variegated effect at will and in more ways than one. The use of double glazes to produce new and curious effects is characteristic of the period. The second glaze was applied in various ways by blowing, flecking, or painting it over the first. The Chün glaze of the muffle kiln belongs to this type if it has, as I think, been correctly identified with the blue green dappled with crimson on Fig. 4 of Plate 128; and the bird’s egg glazes mentioned on p. 217 belong to the same class.[439] Others of a similar appearance, though not necessarily of the same technique, are the tea dust (_ch’a yeh mo_) and iron rust (_t’ieh hsiu_). The tea dust glaze has a scum of dull tea green specks over an ochreous brown or bronze green glaze, applied either to the biscuit or over an ordinary white glazed porcelain; and it seems to have been a speciality of the Ch’ien Lung period, though there are known specimens with the Yung Chêng mark and many fine examples were made in later reigns. But neither this glaze nor double glazes in general are inventions of this time. It would be more correct to speak of them as revivals, for the early Japanese tea jars, which are based on Chinese originals, illustrate the principle of the double glaze, and there are specimens of stoneware as old as the Sung if not the T’ang dynasty, with dark olive glaze flecked with tea green, and scarcely distinguishable from the Ch’ien Lung tea dust. It is stated on the authority of M. Billequin (see Bushell, _O. C. A._, p. 518) that a “sumptuary law was made restricting the use of the tea dust glaze to the Emperor, to evade which collectors used to paint their specimens with imaginary cracks,[440] and even to put in actual rivets to make them appear broken.”