Glass with Class

Enameling is a time-honored process that’s great for bringing elegant color to metal jewelry.

Six forms of glass-based (vitreous) enameling have been developed over centuries: champleve, cloisonné. Limoges, plique a jour, basse-taille and grisaille.

The name “champleve” comes from the French work for “raised plane.” In this method, the enamel colors are applied to depressed areas in the base metal. The depressions are created by etching or engraving the metal, or by sawing out areas of a second metal sheet and soldering this to the base sheet. The process was first done by the Celts in the British Isles during the 3rd century A.D.

The word “cloisonne” comes from the French word cloison, meaning “cell.” Cloisonne is a multicolor enameling process in which enamel colors are separated by thin metal wires that form the design or “cells.” The wires not only contain the different colors, but they also act as decorative elements in the design, help anchor the enamel to the base and share the stress of the intense heat required to melt the enamel. Examples of early cloisonne date from the 4th century A.D. in the Byzantine Empire through the 12th century A.D.

Limoges, also known as painted enameling, was developed around 1500 A.D. by the Penicaud family of Limoges, France. Ground, wet enamels are applied freely onto the metal base with fine brushes and inlay tools. Areas of colored enamels are laid side-by-side in thin, uniform layers. When fired, the different colors do not intermingle. Further effects can be gained by using transparent, opaque and opalescent enamels, as well as gold or silver foils.

Plique-a-jour, or backless enameling, is another technique. In one method, small openings are cut in a metal sheet, but no base is used. Transparent enamels are used to fill the cut-out spaces, and then the piece is fired. The result is a small stained-glass window, since light passes through the transparent enamel.

Basse-taille (literally, “low-cutting”) enameling uses a sheet of etched, engraved or impressed metal covered with a thin layer of transparent enamel so the design on the metal can show through.

In grissaille (gray) enameling, fine, opaque white enamel is sifted onto a pre-fired black or dark enamel base. A design is scratched through the unfired white enamel to reveal the dark base, and then it is fired. Additional areas of white are built over the first layer in subsequent firings to improve the details and to add to the depth of the design. Many fine examples of grissaille can be viewed in major museums.

Vitreous enameling can produce gem-like works of art that have everlasting quality and beauty.

Forming Enamels
The amounts of borax and lead oxide added to the silica determine the hardness of the enamel. Potash enhances the color, and the amounts of soda and borax affect the elasticity. Different metal oxides produce different colors. For example, red enamels are made from gold oxides. The addition of tin oxide will make an enamel opalescent or pearlized.

To make enamel, all the ingredients are melted together in a furnace for about 15 hours. Then, the molten glass is poured from the furnace and quenched with water. This produces cool, coarse chunks. These are ground and sifted through graded sieves to a size that is somewhat finer than granulated sugar.

There are three different types of enamels: transparent, opaque and opalescent. A transparent enamel has a gem-like depth. An opaque enamel is solid-looking. And an opalescent enamel looks like pale milk-glass. Many different colors and effects can be achieved by firing one color over another or by using different types of enamels next to each other.

The appearance of transparent enamels is affected by their depth or number of layers, as well as by the texture and color of the metal underneath. The appearance of opaque enamels is not affected by these factors. Opalescent enamels are semi-transparent; when overlaid on a darker transparent or opaque color, they appear as a fine haze of that hue.

Enamel powder is applied to metal by one of several methods. In the wet-packing method, small amounts of enamel colors are washed with distilled water and wet-packed with the use of a fine brush or a spatula onto the metal. Then, the piece is thoroughly dried and placed in a kiln.

Enamels are fused (melted) onto metal in a kiln at firing temperatures ranging from 1300°F to 1600°F (the 1450°-1500° range is best for jewelry). After firing, the piece is removed from the kiln and allowed to cool at room temperature.

Note: An enameled piece needs to be heated until it melts enough to fuse with enamel or metal underneath, but not so long that the color “over-fires” and darkens or the enamel layers break up. So keep a “close watch,” observing the piece in the kiln by cracking open the kiln’s door.

Additional coats of the same or different enamel colors can be applied to a piece. Sometimes 10 to 20 firings are required to achieve the desired results. Generally, the first layer of enamel is heated until it is smooth in texture. Subsequent layers are fired in the same manner, as long as the piece isn’t over-fired.

Metals for Enameling
The physical properties of glass enamels can be controlled to permit bonding to metals such as copper, silver, gold, platinum, steel, cast iron and aluminum. But, jewelry enameling is most often done with copper, silver or gold. Platinum’s low thermal expansion makes it difficult to use for enameling, although platinum alloyed with ruthenium, which acts as a hardening agent, is easier to use.

Copper is a very stable metal for enameling. It tends to warp less during firing, and it accommodates the expansion rates of the enamels. Copper also can be quite thin and still retain its shape and stability against cracking. However, when used for enameling, copper needs to have a layer of enamel called “counter-enamel” applied to the underside.

Enameling on copper is different from gold and silver in that each firing produces oxidation called “fire scale.” The fire scale must be sanded off between the application of the enamel and the subsequent firings.

Another difference is that dark, transparent colors do not appear as light on copper as on gold or silver, so a layer of colorless enamel called “flux” has to be fired onto the copper prior to wet-packing these colors.

In cloisonne enameling, gold and silver wires can have eutectic reactions during firing. However, a “flux” layer of enamel acts as a buffer against eutectic reactions.

Fine silver (.999) is wonderful for enameling. It does not oxidize during firing and, therefore, stays bright, reflective and clean. It can be easily cast into three-dimensional pieces and enameled. Since it’s not as stable as copper, a fine silver piece must be thicker. Also, if a cast fine silver piece is thick enough, it does not have to be counter enameled.

If a piece that’s cast in sterling silver is to be enameled, it must have a “skin” of fine silver brought to the surface. This is accomplished by annealing and pickling several times.

Gold is often used for enameling. Transparent enamels, particularly reds, greens, blues and yellows, look great over gold, especially reds. The gold to be used under enamel has to be 14k or 18k green gold, or 22k or higher yellow gold. Otherwise, the zinc in other golds may cause the enamel to peel off of the metal. Green gold can have following compositions:
(100 grams of 14k green gold = 58.4 grams 24k gold + 31.1 grams fine silver + 3.4 grams copper + 7.1 grams nickel.)

(100 grams of 18k green gold = 75 grams 24k gold + 25 grams fine silver.)

If soldering is required after the gold or silver piece is cast, do so before enameling the piece. Remember, you must use a solder that flows above the temperature in the kiln.

Prior to enameling, the piece must be thoroughly cleaned and the fine gold or fine silver brought to the surface. This is accomplished either by repeated pickling in a sodium-bisulfate-based solution at 180°F in a crock-pot or by bombing with a cyanide-peroxide solution if such equipment is available.

After enameling, you will notice that the unenameled portion of the piece has oxidized. Bomb or pickle the piece again. If the piece is gold, sterling silver or copper, the unenameled portion may be carefully polished using rouge and a soft buff with a flexible-shaft machine (to avoid cracking or chipping of the enamel). If the piece is made of fine silver, a light polishing on the unenameled areas is all that is necessary.

AJM, May 1994

Quick Tips For Jewelry Enameling

Suggested Metals for Jewelry(Gold: yellow gold of 22k or higher; 14k or 18k green gold.)
(Silver: fine silver (.999) or sterling silver (.925)(Copper)

Preparation of Metals
Gold: Anneal the gold, and pickle and rinse it several times. Use a Fiberglas brush until a high shine is obtained. Rinse in water.
Silver: Anneal and rinse once for fine silver. Sterling silver is annealed and pickled several times, then rinsed in water until it appears “dead white.”
Copper: Anneal copper and pickle it until all fire scale is off. To get a high shine, just brush under water with a Fiberglas brush (no soap). The edges of the copper object will get fire scale between firings. This has to be removed each time with sandpaper before a new application of enamel is done.

Preparation of Enamels
Enamel powder is spooned into small beakers or shot-glasses. Distilled water is stirred into the beakers. Then, the cloudy water that rises to the top is poured off until the remaining water appears clear. Next, sop up the remaining water in each beaker with a paper towel. Finally, add a few drops of an adhesive solution so the enamel can be wet-packed.

Application of Wet Enamel
The enamel is applied to the surface of the object using a fine, sable brush. Don’t try to use the brush in a “painting” manner, but rather like a “transporter” of the glass frit (granules), called wet inlay.

The colors will appear just where they are placed. They will not run or blend unless you mix them on the surface of the object. Sometimes a gentle tapping of the object will even out the wet inlay. Dry the piece thoroughly before placing the object in a pre-heated kiln.

Application of Dry Enamel
An adhesive solution is brushed or sprayed onto the surface of the metal. Next, the enamel is “dusted” onto the metal surface using an 80-mesh sifter made for this purpose.

Then, the piece is dried and fired. This procedure gives an even overall surface application.

Kiln Temperatures
The ideal firing temperature for jewelry is 1450 F to 1500 F. Here are various temperatures and their corresponding kiln appearances:

1300 F – 1400 F: the kiln glows dark red.
1400 F – 1450 F: the kiln glows cherry red.
1450 F – 1500 F: the kiln glows bright cherry red.
1500 F – 1600 F: the kiln glows light orange-red.

Only use solder that melts above the firing temperature in the kiln. All post, beads, bezels and findings should be soldered with extra-hard solder.

It is not wise to use gemstones/pearls in the object to be enameled since the heat of the kiln can destroy them.

After the desired effect has been achieved, the enameled object is cooled at room temperature.

‘Stoning’ the Surface
If the surface of the enamel is to be level, slight “stoning” is required, which will leave a matte finish. Do so first with a medium Carborundum stone and then with a fine stone. Then, use a Fiberglas brush under running water (no soap). Refire the enameled piece to bring out a shiny surface, if desired. | 800-759-9997 | (fax) 800-616-9997