TECHNIQUE

ENAMEL

Enamel

Italian: smalto

French: smalt

German: schmelzen (merge)

Substance of vitreous nature consisting of a mixture of silicates, potash, silica, soda, aluminum, quartz, feldspar, borax and metallic ores containing phosphors as well as numerous metal oxides. The preparation of the base material of the enamel takes place in melting furnaces in which loading the ingredients mentioned above.

The mass is heated to temperatures varying, depending on the opportunity, between 1000 ° and 1200 ° C until the formation of molten glass; follows a sharp water cooling. It is at this point that the material is ground finely taking the name of “frit”. The coloration of the base material is given by the addition of the metal oxides in different percentages that will not impair the transparency. They are mixed with “fried”, and then washed with distilled water for a long time to remove any residual dust contamination. The whole work is then remelted and cast in brackets to be able to store in blocks. Before the use it must be finely ground and again washed with distilled water.

There are about 700 different colors of enamel, but in practical use today is limited to about two hundred. However, the layering of different colors allows an almost infinite range of combinations and nuances that can degrade, even on the same object, the darker shades to lighter ones, and vice versa.

The object that you want to realize that may then be covered with enamel, must be built not just taking care of details in relation to the subsequent application of powdered glass.Assuming the case that it should be silver, care should be taken that the sheets have a thickness such as to withstand the high temperature “cooking” of the enamel which is not too far from the melting point of silver.Even the title of the metal must be chosen depending on the type of enamel to be applied, because some colors have made different color depending on the greater or lesser quantity of the alloy contained in the metal. The welds must also be such as to prevent deformation of the object exposed to the temperature of repeated firings for the liquefaction of the different colors of the enamel.

The larger, finally, is the object and the surface to be coated, the greater effort and attention will be needed to ensure that no record distortions and depressions of the sheets treated. The surfaces to be coated must be surrounded by a step at a slight angle, which can contain the liquid glaze.Typically you use to dig the plate to create usable space, while other times you fillet weld around the plate to be enamelled. The latter procedure, however, on silver, involves risk because the enamel can come into contact with the welding and staining or, worse still, crashing.The two processes described are respectively the “champlevé” and the “cloisonné”. The latter, however, also provides for the application of a metal mesh arranged according to the decorations provided which, located on a first layer of enamel generally white base, delimits the field of the different colors affixed later.

The surface to be coated with a transparent glaze is worked to “basse-taille” with decorations made by incision, often by hand, but often with a “guilloche”: a particular incision, partially mechanical, it achieves with straight lines, wavy, twisted, a myriad of different designs under the clear coat that create highly effective chiaroscuro effects. Often overlaps with the incomparable hand of the engraver “guilloche” infinitely various reasons, aimed at creating a wider disparity and amazing designs.

Very nice especially the hand-engraved reproducing landscapes, architecture, paintings from the Renaissance period.Finally, before moving on to the stage of enamel, each object must be cleaned with brushes and pickling acids with special care because, especially working the silver, not all the metal oxide glazes turn out to be compatible with the oxide of silver, for which it is necessary to eliminate it completely or at least with extreme care to avoid direct contact with the metal of certain colors, interposing a layer of transparent enamel.

The application usually takes place by deposition of the powder, for subsequent melting in the furnace and for final cooling with subsequent vitrification. During the process you need to get a firm adherence to the glass part of the area concerned. The glazing can be “open”, that is visible in transparency, or “night”, that is applied on a metal support (gold, silver, copper, etc.).. This second technique is the most common and is built according to different methods among which the best known are: the “cloisonné”, or partitioned (or alveoli of the report) and “champlevé”, or engraving (or alveoli d ‘ recess). In champlevé the alveoli that host the enamel is obtained directly from the bottom metal through the excavation of seats (alveoli from the raised edge); in Cloisonné instead the seats are made by the application of segments of metal wire (cloisons), generally made of gold and silver.A derivation is the later of cloisonne enamel days (or “watermark,” or “cathedral”), very delicate, where the partitions are welded cloisonné (= compared) between them and non-fixed (= lying) on a slab, but instead left free, as in stained glass, these glazes are brighter and more transparent than those deposited on plates.Another important and fascinating process is one that leads to the creation of translucent enamel, or “basse-taille”, which combines the technique of enamel with that of relief: it is based on the principle of spread a thin layer of colored enamel and transparent of a metal surface already engraved (hand or guilloche) in bas-relief, so that the unevenness of the relief produce delicate effects of light depending on the greater or lesser depth of the relief.Another very effective technique is called enamel “en ronde bosse”, suitable to be applied to the enamel surfaces in the round, such as figurines, eggs etc.. This technique is particularly difficult and delicate because the glass part is still fluid, at high temperature, must be made to adhere to non-planar surfaces, and it takes great skill and attention to ensure that it does not coli downwards, or solidify second different thicknesses, resulting in shades unwanted color.

A place to stand alone occupies the “painted enamel”: its support is usually a precious metal that is covered by a smooth layer of enamel that serves as background for the painting. After the first firing is executed design, according to the technique known as “grisaille” or as one of the thumbnail. The enamel is deposited on metal surfaces in a number of very thin layers. To lay it perfectly using depositaelo with a brush when the powder is still wet, then dries out the excess water with paper towel and let it dry completely then. At this point, the enamel is only a very fine powder lying on the metal. It then proceeds to the cooking which is carried out, depending on the colors of the situations or technical-productive, at temperatures ranging from 680 ° to 800 ° C in order to determine the complete liquefaction of the powders of the crystal. For firing the furnace is first brought to a temperature of about 600 °, after which it is switched off; the object, previously constructed and covered with enamel powder, is inserted supported by refractory tiles that surround and support the strictly vertical surfaces to avoid possible deformations caused by the high temperature.At this point the oven is turned on again and the temperature allowed to rise slowly to the desired level. The technical data is not always valued the experience of the master craftsman who, looking through the peephole and observing the condition of the item, decides the time of extraction from the oven.The cooling of the metal and enamel must be in a natural way while artigian or with special grills, and taking care not to touch in any way, enamel, preserves the object level, and seeks to minimize its inevitable deformation of the structure metal support.The operation is repeated several times depending on the number of layers of enamel that is necessary to lay, and the number of colors used for decoration. It is not rare case of 10, 12 and even 15 cycles after complete processing. From time to time the enamel surface was polished with carborundum wet lime in water, until the surface is perfectly leveled. If you encounter any reading is done avvallature “filling” with new layers of enamel and cooking all over again. The last cooking leaves the surface acceptably smooth, but not yet brilliant. To achieve this it is necessary “levigarla” with brushes of felt and pumice fine under appropriate water jet.Interestingly, while cooling the silver and enamel undergo contractions so different, if the object has not been achieved with the necessary technical adroitness, the enamel, which cools assumes its glassy nature, can easily break (or, As they say in, “splash”) defeating virtually all the work.It should be borne in mind, moreover, that the difference in cooling rate does not only concern, as is easy to understand, the metal and the enamel, but, although with a much smaller gradient, also the different colors of enamel between them. Moreover, this difference is found, as already said, also in the “point” of liquefaction so that when several colors have to be cooked on the same object is that to start with the lowest melting temperature, in order to avoid that, in the reverse case, the most “soft” burn at a temperature of more than “hard”. At this point the artifact in silver, now definitely enamel, is loaded with several layers of oxide, in the jargon called “peel” as a white, porous, it is necessary to remove with the aid of squeegees, lime, ground joint and finally with stone pumice end: this is a phase of long and delicate process that precedes the finish of the engravings and / or external guilloche, you must be careful not to scratch or chip the enamel, not to heat the object too, to ensure that pastes are not too abrasive, and so on. Pena having to start work again.Generally, finishing a piece of silverware includes a large enameled gold, which enhances the colors applied. The gold plating baths are also special, because they can not be too warm, and the electric current must be given in a limited way, for which the electrolytic solution must be particularly rich in starting.

The ENAMEL “à JOUR” (or watermark, or cathedral) is particularly delicate, fragile and yet fascinating.The miniatures are hand-painted enamel on a uniform is usually white. Using the same colored glazes, but much more finely ground, which are mixed with special oils to form an endless palette of colors. The paint should be dried slowly on electric stoves so the oil evaporate, but must also be baked at high temperature for several times the amount of color is never too great a risk of spread with the liquidation. A beautiful miniature varies from 20 to 50 firings.Another interesting example is the decoration can be inserted between the different layers of enamel “PAILLONS” (=straw) PURE GOLD thickness of a few hundredths of a millimeter, usually depicting leaves, flowers, stars, various reasons, but always very small, which, if applied at a certain distance from each other on a bottom of a dark color, and subsequently covered by a transparent layer, achieve a decorative effect at times particularly pleasant. The use of the support aureus, rather than the silver one, in the production of enameled objects presents problems much smaller, both because gold is steel, and because of its higher melting point, and because it must be gold in the final stage . The cost of the metal is now obvious, however, severely limited in its wider dissemination.