Basse Taille. This is the process of engraving the ground, which is to receive translucent enamel, so that the lines made by the graver will show up through the translucent vitrified coating and produce a greater play of light, or define patterns, the veining of leaves, the marking of petals, the lines of draperies, etc. The French enamelers of the eighteenth century habitually employed the process, and Indian enamelers preceded them by at least a century, while its invention is ascribed to an Italian, John of Pisa, in 1286. This chasing or engraving upon gold or silver for the purpose of showing graduation in the vitreous color to be applied is akin to champlevé.
Plique à Jour. Enamels of this sort consist of certain screen-like objects in filigree with their unbacked cloison divisions filled up with translucent enamel. Plique à Jour enamel may be compared to stained-glass windows, the principle being the same, only carried out on a miniature scale. An excellent example of this is a fifteenth-century cup in the Victoria and Albert Museum, while the Crown of St. Stephen, dating from 1072 A.D., would appear to be the earliest known work of the sort that has survived. The Russians of the nineteenth century so perfected the process that plique à jour enamel is often called Russian enamel. Doubtless the forming of cups, caskets, and other precious objects of gems in unbacked mosaic suggested the style, and the jeweled cup of Chosroes to be seen in the Bibliothéque Nationale, Paris, may well be considered a forerunner of it.
Encrusted Enamel. This may be defined as enamel used to enrich raised and modeled gold-work where this vitreous color is neither entrenched, as in cloisonné or in champlevé, nor painted, like Limoges work, on a flat field. The craftsmen of the Renaissance, both in Italy and in France, produced exquisite jewels of encrusted enamel, imitated by the Florentine jewelers of to-day who display their wares along the shops of the Ponte Vecchio. Painted enamels in this group may be sub-divided as follows:
(A) Those works which have vitreous colors added here and there to subdue, to correct, or to outline and decorate enamel surfaces, such as the pale yellows added to soften glaring whites, red to restore a color unsuccessful in the firing, outlines of plants and other forms and inscriptions. Used in combination with both cloisonné and champlevé, and later to add further decorations to basse taille surfaces.
(B) Those works painted with successive firings of translucent or transparent colored enamels over a primary enamel ground that first has been fused to its metal field of gold, silver, or copper. Limoges enamels of this sort, whether in color or in grisaille (gray), as also are the much-neglected enamels known as Venetian enamels.
So much for the general broad divisions of enamels, though it must be borne in mind that there was often employed in the working out of a single object more than a single process. As color plays so important a part in the evolution of the history of enamels, the following table may prove useful to the collector as determining the more important colors of the enameler’s palette at different periods in the history of the art:
COLORS AND PERIODS
Greek Work. The colors used by the Greeks were opaque white, blue, and green.
Barbaric Work. British, Gallic, Celtic, and Roman-Provincial enamelers used scarlet, cobalt blue, dark green, yellows through light shades to orange and to ochre; white, black, and possibly turquoise.
Early Byzantine Work employed opaque scarlet, coral, white, black, and translucent sapphire blue, emerald, green, ruby red, and manganese violet.