In the case of a purely modern imitation, the faker’s art consists, as usual, in giving the piece a convincing appearance of age, once the actual making has been performed. This is generally effected by exposure to apparent ill-usage, by greasing and smoking the object, then cleaning it and repeating the operation over and over again till the dirt has penetrated into all the cracks, or by burying it in a manure-heap and letting it remain till it has lost all freshness. There are also chemical ways by which the glaze is eaten and its composition altered. It is a fact that fluoric acid readily eats the glaze just as it dissolves glass, and under certain circumstances the lead in the glaze under the form of silicate changes under the action of hydrosulphuric acid. Cracks or a regular network of _craquelage_ are generally produced on new ceramics by the same principle as they are obtained on oil paintings, namely, by producing artificially a difference in the shrinkage capacity of two superimposed layers. In oil painting it is the layer of pigment and of varnish, in the case of pottery the two layers are represented by the baked clay and the glaze. If the clay has a smaller shrinkage than the glaze, in the second firing of the piece to melt the glaze, the latter will dry in a network of cracks like those on Chinese or Japanese vases, which are reproduced by this method. Reversing the game, the glaze peels off here and there in drying and produces the imperfections sometimes desired on imitations of old and damaged pottery. An artificial disproportion between the shrinkage of the clay and the glaze is usually obtained by modifying the quality of either the one or the other. Does the clay shrink more in the firing than is desired, the ceramist generally mixes it with non-shrinking elements such as powdered brick, or even another kind of clay which he knows must shrink less on account of its composition, although it may not be suitable in colour and quality. By this same modification of the composition the shrinkage of the glaze is increased or diminished. Glazes are generally composed of a combination of silex, furnished by sand, and oxide of lead with the addition of some flux such as borax. With an increased quantity of silex in the composition of the glaze the shrinkage capacity is diminished. Consequently a predominance of the other elements, lead, flux, etc., produces the opposite effect, namely, giving the glaze a greater shrinkage capacity. Some workmen prefer to modify the quality of the clay to obtain the desired _craquelage_, others find it more practical to modify the glaze.