A process of connecting or covering metal with glass. The origin of enameling can be traced to ancient times when vitreous (made from glass) enamels were used on and in metalwork. Enamels are typically applied by dry sifting the particles onto the surface or by wet packing the enamels into channels or depressions in the metal.
Some Techniques of Enameling are:
The following has been borrowed from KC's enamels  His research and in-depth explanation of each process is valuable. Check out the link for more information on Enameling processes! It is a great resource, it also has projects to try.
- Basse Taille: French for “low cut.” A technique in which a pattern is created in the metal backing before enameling.
- Camaieu: also called “en camaieu,” a term dating from the mid-18th century describing a grisaille-like technique which uses a buildup of white enamel to create highlights and light areas. However, instead of using a black background, as in grisaille, transparent enamel is laid in first, beneath the whites. This technique is frequently used on snuffboxes, watches, and medallions.
- Champleve: French for “raised field” or “raised plain.” A technique in which enamel is inlaid into depressions in the metal, leaving metal exposed. The depressions are typically made by an etching process, although other methods exist. First done in the 3rd century AD by the Celts decorating their shields, this technique has been one of the favorite forms of enameling.
- Cloisonne: French for “cloison” or “cell.” A technique in which metal wires are bent to form a design; enamel is then inlaid into the resulting “cloisons.” Although this can be done in copper, contemporary cloisonné is most frequently done in silver or gold. The Byzantine Empire, 6th century AD, was the setting for gold cloisonne pieces of a religious nature. In the same time frame, the Japanese were producing scenes of nature. In China, cloisonné has been used since the 13th century AD.
- Gimbari Foil: a technique, developed in Japan, using a foil design made with an embossing plate. This is an excellent technique for reproducing a design, as the embossing plate is reusable. It somewhat has the look of cloisonné; however, the “lines” are not wire, they are embossed foil.
- Grisaille: French for “greyness.” A form of “painting” with enamel in a monochrome, using a black background with a buildup of white overlays.
- Guilloche: (gee-yoh-shay) French for “engine-turning.” Engine-turning is the mechanical cutting of lines on metal to create a design. Because the pattern is engraved, the reflection of light through the over-coating of transparent enamel is enhanced, and its brilliance can be seen as the piece is moved from side to side.
- Impasto: a technique in which acid-resistant painting enamel is applied to a bare metal surface, then fired. Multiple layers can be worked to build up a relief design, which can be sculptural in effect. Finally, the piece is covered with a transparent color. Other colors then can be added in thin layers only.
- Limoges: a technique of “painting” with enamel in which different enamel colors are put next to each other without the separation of wire or surface metal.
- Plique-a-jour: French for “membrane through which passes the light of day.” A technique that resembles miniature stained glass and is reminiscent of its Art Nouveau and old-world influences. There are two basic methods of plique-a-jour: surface-tension enameled and etched-enameled.
The surface-tension method has two different styles of metal construction: the first is pierced. The second style is filigree or skeletal framework. The filigree style was first used in the 11th century and accepted all over the world. The etched-enameled method is called Shõtai-Jippõ, and sometimes “crystallized cloisonne” in Japan. It is done somewhat like cloisonné with a copper backing and silver wires, but after the piece has been finished, the copper backing is etched off. Plique-a-jour pieces, because of the open back, are more fragile than other types of enamels.
- Raku: a technique in which hot enamel that includes oxides is smoked, resulting in iridescent colors. The technique can be used with or without silver nitrate crystals.
- Sgraffito: a technique in which lines are drawn through a layer of unfired enamel, exposing the fused enamel (or bare metal) underneath.
- Silkscreen: a technique in which designs on material mesh, such as silk, polyester, or nylon, are transferred onto an enameled base; this is similar to silk screening on cloth.
- Stenciling: a technique in which a design is cut into a material, such as paper or Mylar®, through which the enamel is applied to, or removed from, the metal. Thus, the “holes” that are cut can be either the positive or the negative space of the design. That is, one can sift enamel onto the metal, lay down the stencil, then use a brush to remove the enamel in the cut-out area (negative). Or, the stencil is laid on the metal and enamel sifted into the cut-out area (positive).
- Torch-fired: a method of enameling in which a torch is used for the heat source, instead of a kiln.
Although each of these techniques can be used by themselves, two or more can be combined in one piece.
In addition, enameled pieces can be enhanced by decorative additives such as:
- China Paints: low-fire compatible ceramic materials that can be used on the top surface of enamels.
- Over-glazes and Under-glazes: finely ground pigments used either over or under the regular enameling layers. Under-glazes are particularly effective in a bass-taille design.
- Copper Screen or Pot-scrubber Mesh: elements for use on top or under transparent enamels, giving a wonderful texture to a piece. The screen can be used to give an interesting grid effect. If used slightly under the enamel surface, when the surface is ground down, screening can give the effect of woven fabric as the stoning picks up the high parts where the warp wire crosses over the weft wire, leaving copper glints that give a textured pattern on the surface.
- Decals: design or picture printed on specially prepared paper for transferring an image to enamel, glass, wood, etc.
- Foil and Leaf: come in both fine silver and gold. In addition, leaf, which is much thinner, also comes in palladium. These elements can be placed under the enamel or on a top layer. Special foil objects, called paillons, are small pre-shaped designs that have a slight relief to them.
- Gemstones: can be added in an enameled area, using a metal bezel, which adds relief to a flat piece.
- Granules: small grains of fine silver or 22k or 24k gold that can be used for top-layer embellishment of an enameled piece.
- Glass Beads and Balls: can be purchased without holes and fused to the top of enameled pieces.
- Lumps and Threads: “lumps” are odd-formed chunks of colored glass and “threads” are filaments (short or long, thin or thick) of colored glass. Each can be fused into an enameled piece.
- Lusters: metal colors thinly applied on the top layer of an enameled piece. These sometimes fire with a crackle-maze effect, allowing the enamel underneath to show through. Some fire iridescent and some opalescent.
- Metal: small pieces of shaped metal can be added on the top layer of an enameled piece. They are embedded in a similar way to granules.
- Millefiori: cross sections of glass canes that include intricate patterns. Millefiori is best known in Venetian glass objects such as vases, paperweights, and lamps.