The mottled classes owe their appearance less to the difference in the colouring matter than to the manner in which it is applied. They are termed in French _flambé_, and there is no doubt that they were originally accidentally produced. According to the letters of a Jesuit missionary, Père d'Entrecolles, written in the early years of the eighteenth century, such vases were called _Yao pien_ or _transmutation_ vases. Such types, with turquoise colour passing into green, green melting into purple, and amber fading into grey, are suggestive of the permutation of colour harmonies which these transmutation glazes undergo in the furnace. Beside the _flambé_ glazes there are crackled glazes of turquoise-blue, apple-green, or of greyish white. This crackle porcelain is now artificially produced, but it doubtless owes its origin to accident and caprice of firing. [Illustration: POLAR BEARS ON AN ICE FLOE. Modelled by C. E. Bonnesen. Crystalline glaze by V. Engelhardt.] In _flambé_ glazes an English potter, Mr. Bernard Moore, of Longton, has succeeded in producing _sang-de-bœuf_ colour with delightful gradations of tone; unhappily, some of these pieces were destroyed by fire at the Brussels Exhibition in 1910. =Copenhagen produces the First Crystalline Glaze.=--At the Copenhagen factory _grand-feu_ coloured glazes have been developed in a remarkable manner. The crystal glaze, the serpent-skin, the tiger-eye, and crackled glaze, as well as many other varieties, show effects which hitherto have been unknown in porcelain, and have won the admiration of all connoisseurs. The inception of the crystalline glaze was due to Hr. Clement, the chemist at the Royal Copenhagen Factory, and it was owing to the indefatigable energy and experiments of Hr. Clement that, in 1886, the first piece of porcelain with crystalline glaze achieved a record for the Copenhagen laboratory and studio. Since that day other European potters have succeeded in producing crystalline glazed ware of exceptional beauty. We illustrate a fine specimen of the early crystalline glaze of Copenhagen now preserved at the Museum of the National Porcelain Manufactory at Sèvres. It represents a frog on a leaf. "We should like specially to point out," says M. Edouard Garnier, the Director of the Museum at Sèvres, writing in 1894, "a large water-lily leaf on which a frog is imbedded in a thin layer of ice, which it has just succeeded in breaking. We have never seen a more striking example of what may be attained by a purely scientific process applied to art decoration, and we cannot repress the wish that this example may be followed by our modern ceramists." This is one of Arnold Krog's fine conceptions.