The paste used is somewhat fusible; it is coloured pale yellow or pink, more rarely white. According to the effects required it is covered: (1) with colourless transparent glazes (varnishes), which are placed either directly on the paste or over a dip; (2) with coloured transparent glazes (transparent enamels); and (3) with white or coloured opaque glazes (opaque enamels). The three kinds of glaze may be used together, and thus the preceding effects increased and varied.
The varnishes, which are generally plumbiferous, contain on an average 50 to 60 per cent, of oxide of lead with 40 to 50 per cent, of silica, those containing most lead being suitable for the most silicious pastes.
The transparent enamels are prepared with the foregoing varnishes to which are added from .5 to 5 per cent., according to the intensity of colour desired, of colouring oxides. If several varnishes are used together, care must be taken that they melt at the same temperature; this result is obtained by varying the quantity of silica, or by introducing alkalies.
It must be noted that the presence of the metallic oxides modifies the fusibility of simple glazes.
The opaque enamels are most used, because they allow of the colour of the clay being masked. The paste must be calcareous in order that they may harmonise with it. The fluxes used are the oxide of lead, boric acid, and the alkalies; the oxide of tin acts as an opaque substance, and the quantity of it used depends upon the colouring of the paste. Above all, the composition must be such that there are: (1) complete harmony between the paste and the glaze, in order to avoid crazing or scaling; (2) penetration of the glaze into the paste, to ensure a solid coherence between the two substances.
To satisfy the first condition, we have only to fulfil the laws relating to glazes (p. 394). The second is satisfied by noting the mutual action of the substances upon one another, for instance: to place an alkaline (basic) glaze upon a silicious (acid) paste, and, conversely, a silicious (acid) glaze upon an aluminous (basic) paste, for under these conditions there is a chemical combination between the elements of the glaze and those of the paste. As regards physical properties, the paste must be porous enough without being too much so, and the glaze must be very fusible in order that it may penetrate into the pores where the chemical reactions will take place. These properties, which are sometimes contradictory, oblige us to modify the mixtures, and to choose a happy mean. Thus the silicious glazes preferred for aluminous pastes are necessarily not very fusible; the quantity of silica must then be reduced or, if possible, an energetic flux added.
Fig. 865. Sphinx in the Gate of the Palais des Beaux-Arts at the Exhibition of 1878, executed by Loebnitz from the Designs of Paul Sedille, the Architect.
The glazes are usually applied to the unbaked paste, either by immersion, sprinkling, or with the brush, or, for large monochrome surfaces, by insufflation. Some more delicate pieces are glazed when in biscuit or slightly heated.
The decorative effects obtainable are increased by combining opaque enamels with transparent enamels, or with dull enamels produced by adding a large proportion of silica to the glaze, and so diminishing its fusibility. Instead of applying the enamel to all parts of the piece, the natural colour of the clay may sometimes be left visible in certain places, or it may be covered with gold-leaf, which thus adds its brilliancy to that of the enamels.
Lcebnitz was one of the first to make ceramic products of this kind, and the earliest example was the decoration of the monumental gate forming the entrance to the French Beaux-Arts at the International Exhibition of 1878; Fig. 865 shows a part of it.
The same ceramist executed in a similar style the large panels which decorated the porch of the Palais des Beaux-Arts at the Exhibition of 1889 (Fig. 866).
That Exhibition (of 1889) presented a considerable choice of the most diverse ceramic products. The Palace of the Argentine Republic (Fig. 867) especially attracted attention by its remarkable ornamentation, consisting only of iron and clay, and designed by the architect Bellu.
Fig. 866. La Virite; a Decorative Panel from the Torch of the Palais des Beaux-Arts, on the Garden Side, at the Exhibition of 1889 (Lcebnitz).
The panels forming the bases of the windows (Fig. 871), the metopes (Fig. 870), entrance arcades, knobs and tops of facades (Figs. 868, 869), were executed by Loebnitz. Muller had provided bricks and enamelled friezes, such as those on the facade pillars, called "Eicus " and "Chats".
Fig. 867. Palace of the Argentine Republic at the Exhibition of 1889 (M. Ballu, Architect).
Fig. 873 represents an enamelled frieze with dull ground, "grand feu," executed by Muller, and Fig. 874 is a decorative panel with dull ground and reliefs set off by enamels.
Private buildings, particularly. those intended for special purposes, such as cafes, restaurants, etc., are also decorated with enamelled pottery. It would be easy to mention a great number of examples in Paris of this use of decorative pottery, which is applied inside in the form of panels of facing quarries, and outside in various forms.
Figs. 868 to 872. Enamelled Terra-cotta Decorations on the Palace of the Argentine Republic (executed by Loebnitz).
Many of these decorations, however, are not irreproachable as regards harmony of colours, and the effects produced are not always in the purest taste. As examples we may mention the design of the entrance gate of the Bal Bullier on the Boulevard Saint-Michel, and the facade of the Cafe Riche on the Boulevard des ltaliens. Fig. 875 represents the design of one of the pillars of this cafe; the background is formed of enamelled bricks; the figures and bricks, executed by Loebnitz, are covered with stanniferous opaque enamels in accordance with the traditions of the firm, which has remained faithful to this old-fashioned enamel, and has, so to speak, made a specialty of it.
Fig. 873. Enamel Frieze, "Grand Feu".
Fig. 874. Decorative Panel on Dull Background. (Manufactured by Emile Muller).
The English naturally make great use of architectural faiences in the form of friezes (Figs. 876, 877), decorative panels (Figs. 878 to 880), etc.
Fig. 875. La Danse, executed in Cutlery by Loebnitz.