Vitreous enamel is a comparatively soft glass, a compound of flint or sand (silica), red lead, and soda or potash. These materials are melted together, producing an almost transparent glass, with a slightly bluish or greenish translucent tinge; this substance is known as frit or flux -- or, in France, fondant. The degree of hardness of the frit depends on the proportions of the components in the mix. Enamels are termed hard when the temperature required to fuse them is very high; the harder the enamel is, the better it will withstand atmospheric forces.
Clear frit is the base from which colored enamels are made, the coloring agent being a metallic oxide, which is introduced into the frit when the latter is in a molten state. The brilliance of an enamel depends on the perfect combination of its components and on maintaining an equal temperature throughout its fusion in the crucible. The color of many enamels is achieved by a change in the proportion of the components of the frit rather than by a change in quantity of the oxide. For example, turquoise-blue enamel can be obtained from the black oxide of copper by using a comparatively high proportion of carbonate of soda; in the same way, a yellowish-green enamel can be obtained from the same black oxide by increasing the proportionate amount of red lead.
Clear frit is also used to make opaque enamels; the addition of calx, a mixture of tin and lead calcined, renders translucent enamels opaque. White enamel is produced by adding stannic and arsenious acids to the frit, the quantity of the acid affecting the density, or opacity, of the enamel.
The heated enamel, after being thoroughly stirred, is usually poured out onto a slab and allowed to solidify into cakes of approximately four to five inches (10 to 13 centimeters) in diameter. For use, each cake must be pulverized into a fine powder with a pestle and mortar; the powder then has to be subjected to a series of washings in distilled water until all the floury particles are removed. The metal, on which the powdered enamel is to be spread, is cleansed by immersion in acid and water. All trace of the acid is then removed by washing and by drying in warm oak sawdust. After the wet powder has been spread on the metal, it is allowed to dry in front of the furnace before it is carefully introduced into the muffle of the furnace (a compartment protected from the flame), where it is heated to the point at which it fuses and adheres to its metal base. The firing of enamel takes only a few minutes, and the object is then withdrawn, allowed to cool and then stoned or polished.
The various techniques practiced by craftsmen in the past differ mainly in the methods employed in preparing the metal to receive the powdered enamel.
Basse-taille
The Basse-taille (pronounced "Boss-tie") technique (a.k.a., "Guilloché" and "Engine-turn" enamel) is a sophisticated extension of the champlevé method, for again the metal surface has to be cut away and filled with enamel, but here there are two major differences. First, within the area that has been cut away to receive the enamel, a design or figural composition is chased (chiseled), or sometimes engraved, in low relief. Because the highest point of the relief is below the general surface of the surrounding metal, the enamel, which is level on its outer surface, lies in varying thickness over the modeled surfaces of the low relief. Second, because the colored enamels used in this technique are translucent, the composition of the low relief shows through; and, since the metal used is normally gold or silver, the light is reflected back through the translucent enameling, adding a brilliant tonal quality to the enamel, just as sunlight enhances the beauty of a stained-glass window. The effect of the reflected light varies according to the thickness of the enamel lying over the undulating surfaces of the low relief; consequently, an impression of plasticity and of three-dimensional modeling is created by the subtle variations in tonal strengths of the enamel colors, which range from bright highlights to the rich tones of the deep recesses.
Cloisonné
In the Cloisonné (pronounced "Cloy-son-nay") technique, thin strips of metal are bent and curved to follow the outline of a decorative pattern; they are then attached, usually soldered, to the surface of the metal object, forming miniature walls that meet and create little cells between them. Into these cells, the powdered enamel is laid and fused by heat. After it has cooled, the surface can be polished to remove imperfections and to add to the brilliance.
Champlevé
This Champlevé (pronounced "Sham-pluh-vay") technique is the opposite of the cloisonné process: instead of building up on the surface of the metal object, the surface is gouged away, creating troughs and channels separated by thin ridges of metal that form the outline of the design. The troughs are filled with powdered enamel and fused. The champlevé technique requires a thick metal base and therefore is used more often on tombac, copper and other base metals.
Painted Enamels
This technique differs fundamentally from the preceding three in that the various colored enamels are not separated from each other by metal strips or ridges. Although these enamels are still applied in their wet, powdered state, the adjacent patch of colored enamel is first allowed to dry to avoid one running into the other and so blurring the outline between them.
The metal is cut with shears into a plate of the size required and slightly domed with a burnisher or hammer, after which it is cleaned with acid and water. The enamel is laid equally over the whole surface both back and front, and then the object is fired. The first coat of enamel being fixed, the design is delineated by drawing with a needle through a layer of wet white enamel or any other that is opaque and most advantageous for subsequent coloration.
In the case of Grisaille (pronounced "Grieh-ss-eye") enamels, the white is mixed with water, turpentine, spike oil of lavender, or essential oil of petroleum and painted over a dark-enamel ground. Light areas of the design are painted thickly; gray areas, thinly to allow the dark ground to tone the white pigment. The technique creates a strong contrast between light and shade, creating an impression of low relief. The scenes in grisaille are sometimes rendered more subtly by hatching, executed with a pointed tool or needle to reveal the dark enamel beneath.
In colored painted enamels, enamel colors are spread over the grisaille treatment; when fired, parts of the surface are heightened by touches of gold, usually painted in thin lines, like hatchings. Other parts can be made more brilliant by the use of foil, over which the transparent enamels are placed and then fired.
Taille d'epargne
The Taille d'epargne (pronounced "Tie-duh-parn") technique describes a process of cutting or carving 'sparingly,' into a grounding with the surface left mainly reserved.
For enameling, this style is essentially a reversal of the champleve enamel method as only outlines or shallow channels are sunk into the metal and filled with opaque black, blue or red enamel. The enamel lines are stoned or polished smooth to lie flush with the reserved metal.
The method has been combined with champleve, for example in medieval work when taille d'epargne was used to add lettering and details.
Plique-à-jour
The Plique-à-jour (pronounced "Plick-ah-jewr") technique is designed to produce an effect of a stained-glass window in miniature through the use of translucent enamels. The technique is exactly the same as cloisonné enameling except that the strips of metal forming the cells are only temporarily attached -- not soldered -- to a metal base to which the enamel will not stick. After the enamel is fused and sufficiently annealed, the metal sheet, usually aluminum-bronze, is removed with a few light taps, leaving a network of metal strips filled with enamel "windows." The enamels can be carefully polished to enhance their appearance.
a
vit*re*ous
[Latin vitreus, from vitrum glass]
First appeared 1646
1 : of, relating to, derived from, or consisting of glass
2 a : resembling glass (as in color, composition, brittleness, or luster) : GLASSY <~ rocks>
b : characterized by low porosity and usu. translucence due to the presence of a glassy phase <~ china>
a
trans*par*ent
[Middle English, from Medieval Latin transparent-, transparens, present participle of transparere to show through, from Latin trans- + parere to show oneself]
First appeared 15th Century
1 a (1) : having the property of transmitting light without appreciable scattering so that bodies lying beyond are seen clearly : PELLUCID
b : fine or sheer enough to be seen through : DIAPHANOUS
synonym see CLEAR
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opaque
[Latin opacus]
First appeared 1641
1 : exhibiting opacity : blocking the passage of radiant energy and esp. light
a
trans*lu*cent
[Latin translucent-, translucens, present participle of translucere to shine through, from trans- + lucere to shine -- more at LIGHT]
First appeared 1607
1 : permitting the passage of light:
a : almost TRANSPARENT
b : transmitting and diffusing light so that objects beyond cannot be seen clearly
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Grisaille
A painting technique by which an image is executed entirely in shades of gray and usually severely modeled to create the illusion of sculpture, especially relief.
In the Grisaille enamel painting technique or monochromatic painting, pulverized white vitreous enamel is made into a paste by mixing it with water, turpentine, oil of lavender, or petroleum oil and is then applied to a dark enamel ground, usually colored black or blue. Lighter areas of the design are thickly painted, while the gray areas are obtained by painting with thinner coats to allow the dark background color to tone the white enamel pigment. This technique achieves a dramatic effect of light and shade and a pronounced sense of three-dimensionality. Grisaille enamels were developed in the 16th century in France by the Limoges School of Enamelers.
Limoges School of Enamelers
Any of the enameled products made in Limoges, France, and generally considered the finest painted enamelware produced in Europe in the 16th and 17th centuries. Limoges enamels are largely the work of a few families such as the Pénicaud, Limosin, and Reymond families. The earliest examples show religious scenes in the late Gothic style. But around 1520, Italian Renaissance motifs appeared and became especially characteristic of the work of Leonard Limosin and Pierre Reymond. Painting in grisaille, or monochromatic painting intended to look like sculpture, was introduced at Limoges and became a specialty of Jean III Pénicaud. By the last quarter of the 16th century, the quality of Limoges enamels had degenerated, and the enamelers Jean and Suzanne de Court in particular turned from the soft harmonies of the earlier artists to the use of bright colors enhanced by an excess of metallic foil called paillons, for gaudy rich effects. The Laudin family dominated the production of the ware in the 17th century and were the last major enamelers at Limoges.
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