The email ([ eˈmaɪ̯ ] or [ eˈmaːj ]; South German, Austrian: [ eˈmaɪ̯l ]) or (more often) the enamel ( [eˈmaljə ], [ eˈmaɪ̯ ] or [ eˈmaːj ]; from French émail , from Old Franconian * smalt , related to melt ; also found as fused glass or smelting works ) denotes a mass of inorganic composition, mostly consisting of silicates and oxides , which is produced in a mostly glassy solidified form by melting, fritting or sintering (which means a melting process that is aborted shortly before melting together). This mass, sometimes with additives, is usually applied in one or more layers to a carrier material and melted at high temperatures and for a short burning time, with a coating of the carrier material usually being sought. Enamel is used on metal or glass as a carrier material.
As a synonym for enamel also is glass flux used (but glass flux is the collective name for products manufactured with metal inclusions glasses such as Gold River , Blue River , Green River and purple river for jewelery).
The specification for “enamel” published by the RAL Institute is used to distinguish similar products in the movement of goods . The valid “Definitions for Email (le)” are laid down in RAL-RG 529 A3. All techniques and materials that do not meet this definition, such as ceramic glazes, are not referred to as "enamel". However, word combinations such as "enamel paint" or "enamel paste" are permitted. However, these materials have nothing to do with the email in the sense of this article. In addition to the technical and legal definitions of the RAL institute, the following should be noted on the use of enamel / enamel: The art-historical and artisan technical language prefers the term enamel , which denotes both material and technology as well as a (small) enamelled object or an enameled part .
The protective function of enamel on everyday devices is an innovation of the 19th century. Older enamel works have a decorative character throughout. The first known enamel work is 3500 years old and was found as grave goods in Mycenaean tombs in Cyprus . The ancient Egyptians were also familiar with enamel work, on both gold and iron. The Celts reached another high point in enamel technology in 500 BC. With the blood enamel .
In the Middle Ages , enamel was used in goldsmithing . The art of enamel first flourished around the year 1000 ( cell melting , cloisonné ), possibly promoted by the Byzantine empress Theophanu (compare the cover of the Codex aureus Epternacensis ).
Delicate, flexible gold bands were soldered onto a metal plate in such a way that they gave the outlines of the desired figure. The resulting cells ( cloisons ) were filled with different colored melting powders and heated until the mass melted. This was repeated until the required height of the email was reached. A central workshop for this technology was probably located in Trier . An important example of this art is the Pala d'Oro in Venice . Even in the early days, translucent glass flows were popular, which let the golden metal background shine through.
The Maasland emerged in the 11th century with work using the mine smelting method ( émail champlevé ), the heyday of which was in the Cologne area in the 12th century . Here, were opaque enamels preferred whose surfaces were not separated by lands, but filled in depressions that were lifted with a gouge out of the metal. Later the blue works from Limoges (Limosine enamel) gained in importance until the 13th century and were widespread in large parts of Europe. In the 14th century, the transparent enamel, now applied to a relief-like gridded silver background, returned. The mostly figurative drawing was engraved or cut into small plates in such a way that it formed a very flat but sharply outlined relief, and then the entire surface was coated with different colored transparent enamel. Where the layer was thinner, the silver shone through and gave the bright spots, while shadows predominated in the thicker layers. This gave the enamel work an extremely delicate effect.
A type of enamel processing typical of the early modern era is the painter's enamel , which was created in Limoges in the 16th century. The colored areas are no longer separated by bars or metal parts, but instead the colors that merge into one another and are applied with a brush enable miniature, fine, pictorial representations. In order to avoid tension in the carrier material (and thus cracks in the email), the back of the main image was also covered with email ( contreémail [contre-émail]), which could also be decorated. Important artists are Pierre Reymond , Jean Courtais and Léonard Limousin . In the 17th century this technique was replaced by enamel painting . With her, only the metal oxides are painted onto the white enamel ground and burned on. The procedure was used in France and Switzerland in particular, and also in Germany. Watch lids and tobacco boxes were typical applications of this decorative art. After the decline in enamel art in the middle of the 18th century, a return to church goldsmithing only brought a revival of the old enamel art a century later. This revived medieval techniques, in the later 19th century people also remembered the decorative possibilities of the Renaissance and imitated (not infrequently with the intention of forging) the models of the 16th century. Important sites were Aachen, Cologne, Vienna, Mechelen, Brussels, Lyon and Paris. In the 20th century, enamel art was also revitalized in the craft art schools in line with contemporary trends ( Expressionism , New Objectivity ).
Stimulated by the demand, the Japanese, Chinese and Indians also began to take up and perfect the art of enamel again.
From a chemical point of view, enamel is a melted mixture. Glass-forming oxides are silicon dioxide (SiO 2 ), boron trioxide (B 2 O 3 ), sodium oxide (Na 2 O), potassium oxide (K 2 O) and aluminum oxide (Al 2 O 3 ). The oxides of titanium , zirconium and molybdenum serve as opacifiers . So that enamel adheres firmly to a metallic substrate, it also contains cobalt or nickel oxide. The mostly used ceramic pigments are iron oxide pigments , chromium oxides and spinels .
A distinction is made between transparent and opaque enamels with flowing transitions. In industrial use, the enamel is used as a protective coating, for example for everyday objects or process engineering equipment. The metal is protected from corrosion by the enamel layer . One speaks of "technical email". Enamel is often used to decorate the carrier materials, for example by adding colored oxides . Emails that are used for arts and crafts are called art or tombak email. Decorative enamel is enamel for copper and precious metal enamelling.
Since the enamel layer is more brittle than the metal underneath, it can break or flake off if not handled properly. The properties of the enamel must be matched to the substrate material and the intended use. Factors such as color , adhesion , thermal expansion , chemical reactivity , toxicity , processability and also the price are taken into account in the selection. Enamel must have a significantly lower melting point than the carrier material and the color pigments must not decompose due to the heat required.
Enamel consists of glass-forming oxides and those that provide adhesion to the carrier metal or give it color. A basic email consists e.g. B. from 34% borax , 28% feldspar , 5% fluoride , 20% quartz , 6% soda , 5% sodium nitrate and 0.5 to 1.5% cobalt , manganese and nickel oxide each . The composition of cover enamel differs somewhat from this: 23% borax, 52% feldspar, 5% fluoride, 5% quartz, 5% soda, 2.5% sodium nitrate, 0.5 to 1.5% each of cobalt, manganese and Nickel oxide and 6.5% cryolite . Later in the manufacturing process, 6 to 10% opacifiers ( tin oxide , titanium silicates ) and color oxides are added to this. The substances mentioned are finely ground and melted. The melt is poured into water, quenched and the resulting granular, glass-like frit is finely ground again. When grinding, 30% to 40% water, clay and quartz flour are added. Depending on the type of enamel, there are also the mentioned opacifying substances and color oxides. The resulting enamel slip has to rest for a few days for better mixing before it can be used again.
The objects to be enamelled are annealed, etched in acid , neutralized with alkalis and washed. The base enamel slip is applied by dipping or spraying and baked at 850 to 900 ° C. The enamel layer melts into a glass coating and the objects can then be covered with one or more top enamel layers. These are each fired individually at 800 to 850 ° C. Simple enamels, so-called single-layer enamels, are applied in one work step. Thin-film enamels belong to this category.
Technical enamel is the use of enamelling in technical applications.
When Schilderemaillierung thin sheet updates are used. Enamel is applied to a sheet of steel 2 to 3 millimeters thick and fired. The writing is usually created by means of screen printing or with decals made from enamel powder, i.e. from finely ground enamel frit . In the meantime, it is also technically possible to print enamel slip (finely ground enamel frit suspended in water and thickening agents) on a decal using inkjet printer technology. A final burn-in takes place after the labeling has been applied.
In the case of cell melting (French: émail cloisonné , translated as: enamel with delimited surfaces), bars in the form of flat-rolled wires are bent, placed on edge and soldered on a base plate made of precious metal. The resulting cells are filled with email. With variations, very different effects are possible, including the representation of images. With the bars as contours, the enamel can come into its own as a painterly component. After firing, the bars either remain raised or are then ground down to the level of the enamel and polished. When the cell melts, a layer of enamel, the so-called reverse mail (German notation), must also be applied to the back of the base plate so that the plate does not warp due to the different degrees of thermal expansion of the materials when the glass flow cools.
With window enamel (French: plique à jour or émail à jour , translated as: open enamel), bars are either also soldered together or the desired motif is sawn out of a precious metal plate so that a framework is created. This work is then placed on copper foil or mica , which serves as a hold for the enamel, which is poured into the spaces between the bars and fired. The foil or mica is then removed again so that the enamel is only held on the sides by the webs. The back of the work is then sanded smooth and polished. The resulting decorative enamel is more or less translucent depending on the type of enamel used and has an effect similar to colored glass windows.
In the case of pit smelting (French: émail champlevé , translated: enamel with a raised plate), either two precious metal plates are soldered onto one another, in the top of which a motif or pattern has been sawn out, or a thick plate is made flat by engraving, etching, scraping or other processes linear indentations, which are filled with the enamel. Due to the greater thickness of the metal plate used, no counter-email is required when the pit melts fire. The carrier plate is not under the enamel as in the case of cell melt , but at the same level as the enamel (hence the French term), which is taken up by the pits sunk into this plate.
The pit relief (French: émail en basse taille , that is, translated "flat-cut enamel") is produced in a similar way to the pit melt, but a picture relief is cut into the flat bottom of the pit, usually with a graver. The pit is then filled with transparent enamel (so-called translucent enamel) so that the engraved image remains visible after the fire. In the deep areas it appears darker due to the thicker enamel layer that is created, while in the raised areas it appears more delicate or lighter, depending on the type of enamel used, so that images can also be displayed in this way. Here, too, a counter email is unnecessary due to the thickness of the base plate used.
When Senkschmelz (French. Émail MIXTE ) are with the aid of flat punches recesses in the very thin base plate driven . Then, as with cell melting, these depressions are provided with bars and the resulting cells are filled with enamel and then burned.
Free enamel painting
With this technique, apart from an outer frame, there are no dividers to separate the enamel colors. Otherwise, the structure of the work resembles the cell melt, the enamel colors are applied freely so that they can run into one another more or less depending on the type of material used. The base plate is stabilized by a counter email. In a variant of the enamel painting, the base plate is first coated with a light, usually white layer of opaque enamel, onto which a motif is painted with metal oxide paint and burned. Finally, the work is covered with a colorless layer of enamel.
For the body enamel (French: émail en ronde bosse ) a three-dimensional figure is first carved out of thin sheet metal. This is covered with a layer of reverse enamel on the inside and decorated on the outside with another layer of enamel, which can be colored before firing, as with enamel painting. In a variant, the shape is bent from wire and covered with enamel.
The goldsmith school with watchmaking school in Pforzheim offers training to become an enameller . The German Email Association offers further regular seminars and further training events via the Information and Education Center Email e. V. at.
- Erhard Brepohl : Workshop book enamelling . August, Augsburg 1992, ISBN 3-8043-0154-1 .
- Erwin W. Huppert: Enamelling made easy . Vollmer, Munich 1980, ISBN 3-87876-339-5 .
- Jochem Wolters: The gold and silversmith . Volume 1, materials and materials , 9th edition, Rühle-Diebener, Stuttgart 2000.
- Angelika Simon-Rößler: Color from the fire . Fascination with email. With a historical introduction by Bruno-Wilhelm Thiele. Rühle-Diebener, Stuttgart .
- Gert Lindner: The large mosaic book of works . Mosaik, Munich 1979, ISBN 3-570-06469-7 .
- Leo Lugmayr, Josef Hofmarcher, Friedrich Riess: Email - the material of kings . From raw material to finished product [exhibition documentation]. Riess / Ferrum, Schmiedezentrum, Ybbsitz 2010, ISBN 3-901819-55-X riesskelomat.at (PDF; 5 MB; 90 pages)
- Armin Petzold, Helmut Pöschmann: Email and enamel technology . German publishing house for basic industry, Leipzig 1986; 2nd edition 2001, ISBN 3-342-00657-9 (Deutscher Verlag für Grundstofftindustrie) / ISBN 3-527-30946-2 (Wiley-VCH, Weinheim).