These are exceedingly numerous, for ceramic decoration accommodates itself to every fancy, and the unforeseen results sometimes obtained add a charm to the decoration. The crackling effect is the utilisation of the fault called crazing. The glaze thus formed is covered with another, which penetrates into the crack and brings it out. Mottlings are produced by firing for a considerable time a fusible glaze which runs and makes unforeseen marbling effects. Flashing effects follow from the alternate use in firing of a reducing and oxidising atmosphere. By taking oxides which behave differently under the action of these, for instance those of copper, we get very diverse colourings, which, being unexpected, are very attractive.

The metallic lustres from which the East has obtained such wonderful effects, and which at the present day are treated in such a masterly manner by ceramists, are got by applying metallic salts crushed with vinegar or rich essence, with a brush, to the pieces fired under enamel.

Firing takes place in a muffled kiln at a low temperature, that of early red, in a smoked atmosphere (reducing). The pieces are put in open-work saggers, and come out with a layer of black on them; this is removed, and under it appears the brilliant decoration.

Deck gives the following ingredients : -

Gilded lustre.

Sulphide of copper ... 10

,, iron ... 5

,, silver . . . I

Yellow and red ochre . . 12

Sulphide of copper ... 5

Nitrate of silver ... 2

Colcothar 1

Armenian bole.... 4

Red lustre.

Sulphide of copper ... 2

Protoxide of tin . . . 2

Smoke black 1

Red and yellow ochre . 4

Oxide of copper ... 8

,, iron. . . . 5

Colcothar..... 6

Armenian bole.... 6

Gold and platinum are also used, and on account of their inability to be oxidised, they may be fired in an oxidising atmosphere.

Gold has also been applied under glaze. The effect produced is very powerful, and much more sparkling than gilding over enamel; the difference is of the same kind as that observed between transparent coloured enamels and under-glaze painting. This decoration is obtained by lightly enamelling the pieces and sprinkling them with grains of sand, then firing; gold-leaf, cut to shape, is applied with a stiff brush to the piece, which has been smeared over the required part, with a decoction of quince-pips. The glaze is then laid on, and the piece is fired at a temperature lower than that of the fusion point of gold (10450 C). This kind of decoration requires great care, great taste, and very pure materials. It has been skilfully used by Th. Deck, who has been able to obtain remarkable effects from it.