What is Vitreous Enamel?

Vitreous Enamel is simply a thin layer of glass fused at high temperature on to the surface of a metal.

The word enamel comes from the High German word ‘smelzan’ and later from the Old French ‘esmail’.

The formal definition is : Vitreous Enamel can be defined as a material which is a vitreous solid obtained by smelting or fritting a mixture of inorganic materials.

The Collins English Dictionary defines enamel as “a coloured glassy substance, transparent or opaque, fused to the surface of articles made of metal, glass etc. for ornament or protection.” Vitreous enamel is specifically on a metal base. It is thus defined as a vitreous, glass-like coating fused on to a metallic base. In American English it is referred to as Porcelain Enamel.

It should not be confused with paint, which is sometimes called ‘enamel’. Paints cannot be vitreous enamel. They do not have the hardness, heat resistance and colour stability that is only available with real vitreous enamel. Beware of companies or products implying the use of enamel. Check their credentials and warranties.

Vitreous enamel is part of everyday life and found all around us. You will use it on many kitchen surfaces including cookers, saucepans and washing machine drums. You will find enamelled cast iron or steel baths and clock and watch faces. Out of doors, we use enamel for street signs, Underground station signs, architectural panels, storage and treatment tanks and many other places. It is selected because it is weatherproof, vandal resistant, fireproof and because it lasts and lasts and lasts. Titanic’s Captain Smith’s enamelled bathtub has survived very well under the sea.

The durability of the early advertising signs, still showing the brilliance of the original colours after a hundred years, is one of the best examples of the long-term colour stability of vitreous enamel. Compare them to signs, for example, road signs produced in less durable materials which fade and quickly become shabby. The scourge of graffiti will destroy signs and panelling produced in less durable materials.

Some of the early vitreous enamelled relics date back to the 13th Century BC and the colours are still as vibrant as the day they were produced (click our page on Enamelling History). If you want something where the colour will never fade, use vitreous enamel.

London Underground LogoFollowing the disastrous King’s Cross fire, where combustible materials underground were the major cause, the specification of vitreous enamel for both decorative and functional parts in underground applications is now universal. It cannot burn, in contrast to paints and plastics. The famous London Underground station signs and maps are instantly recognisable uses of this unique product.

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Ceramic Black Enamel Frit

Available in a variety of colors to harmonize or contrast with the vision area, the ceramic black enamel frit is applied to the surface of the glass. Ceramic enamel frits contain finely ground glass mixed with inorganic pigments to produce a desired color.

The coated glass is then heated to about 1,150°F, fusing the frit to the glass surface, which produces a ceramic coating almost as hard and tough as the glass itself. A fired ceramic black enamel frit is durable and resists scratching, chipping, peeling, fading and chemical attacks.

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How to Enamel

Enameling on glass can be achieved in several different methods.

Glass enamels come in a powder form, and it is very uncommon to purchase them premixed. Made from ground glass that is mixed with different colored pigments, this powder is applied in a variety of ways before being fired inside a kiln to make them permanent. There are different COE of Enamels available, so be sure it is compatible with your particular type of glass. In general, glass enamels are different from glass powder in that they contain more intense colorants and other ingredients such as fluxes.

They can be used dry and sifted or sprinkled onto glass, but most individuals prefer to mix them with a binder to form a liquid mixture. With a moist mixture, the enamel can then be painted or airbrushed onto the glass. Use an applicator bottle with this liquid mixture and write or draw on glass.

Low fire enamels can thin out or disappear when fired to fusing temperatures on the surface. There are better results when they are capped. Some of the colors take overheating better than others.

Although this powder comes in a multitude of colors, it is fun to experiment and come up with different shades of color. Add some white to lighten dark colors, while some darker colors can help to add some depth to a lighter tone. By experimenting with these colors, you can achieve an entire rainbow of colors in your enamel art work.

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Vitreous Cover Coat Enamel Frits

We offer Cover Coat Enamel Frits for vitreous enamel coating on sheet steel: Vitreous cover coat enamel frit is a ceramic coating applied to metals, to give complete resistance to atmospheric corrosion, is acid and alkali resistant, abrasion resistant and resistant to water, chemicals, etc.

The ground coat is black or greyish black in colour. Cover coats can be white or any other desired colour. The finish is glossy (like glass) and and suitable for cooking utensils, eating utensils, outdoor sign boards (because of the permanence of its colours), coal chutes (because of its abasion resistance), and chemical reaction equipment.

Our superior cover coat enamel frit MFHC, is a glossy black, almost free from pinholes. Once you have used this frit, you will not want to use any other frit, except, perhaps, an economy frit, which is almost as good as MFHC, but much lower in cost.

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Making the ground coat enamel frit

Ground coat enamel frit are made from a frit based on low melting temperature (2000 to 2500°F) borosilicate glasses. After the glass raw materials are melted (generally in recuperative furnaces) at rates ranging from 5 to 50 tons per day, rapid quenching is used to shatter the resultant glass into small particles. Further particle size reduction is achieved by grinding. The coating is applied using wet suspension or dry electrostatic powder processes, and is then heated to about 1500°F to produce chemical bonding with the metal substrate.

Producers can achieve many colors and formulations in small melting units. Due to the low melting temperatures, the average dwell time is only a few hours. Since the ground coat enamel frit is melted a second time with the metal substrate, seeds in the glass are not a concern as long as the melt is homogenized and all raw material reactions are completed.

Pre-milled ground coat enamel frits now allow enamelers to custom blend their own enamel formulations without using costly milling equipment. The enameler can blend the exact amount required for the job, eliminating waste. Blends can be made almost “just in time,” eliminating the need for a large wet enamel inventory.

Many frit manufacturers have switched from air/gas to oxygen/gas combustion systems to lower their emissions, and this trend is expected to continue. Smelters have become more automated, and larger capacities are being used as product volumes increase through the increased standardization of frits.

Frit manufacturers continue to research coatings to address new applications. For instance, unique appearance characteristics are under development, including metallic lusters to simulate copper metal or stainless steel appearances. Refinements in ground coat enamel frit products are also being made to achieve “easy to clean” oven coatings, as well as infrared reflectivity for faster cooking. In addition, hybrid coatings are being investigated to take advantage of properties provided by both porcelain enamel and organic coatings.

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Direct enamel frits for sheet steel with improved bonding

Base and direct enamel frits have the function of establishing a firm bond between the metal workpiece and the vitreous enamel layer. The enamelling should withstand firing over a wide temperature range, have a smooth, flawless surface and undergo no loss of bonding even after repeated stoving. The development of these direct enamel frits has hitherto taken place empirically. So-called network forming oxides such as SiO2, TiO2, ZrO2, B2 O3 and Al2 O3 were combined with network migrators such as Li2 O, Na2 O, K2 O, MgO, CaO, BaO or fluorides and phosphates and varied until the enamels were satisfactory in the required commercial properties such as fluidity, surface tension, thermal expansion, surface quality and bonding. To improve the bonding of base enamels, heavy metal oxides such as CoO, NiO and CuO and occasionally iron oxide, manganese oxide, molybdenum oxide or antimony oxide were added in varying quantities.

For direct enamel frits, the addition of TiO2 increased the resistance of the enamelling to acid attack, while the addition of ZrO2 increased the resistance to alkalies.

Molten mixtures of base direct enamel frits and enamel frits containing more than 12 oxidic constituents are therefore no rarity. In all multicomponent systems, their development is difficult to oversee and complicated and therefore expensive. The effect of any one component on certain properties of the frits is rarely proportional to its ratio by weight and is independent of other components. An incremental calculation which is recommended for simple types of glass is only rarely possible, e.g. in the case of thermal expansion, and then only approximately. An added difficulty is that several direct enamel frits are usually mixed together and inert substances may be added for enamel commercial requirements or reasons of economy.

For conventional two-layered or multi-layered enamelling, frits with different viscosities and melting properties were combined for the base enamel and inert substances were added to facilitate the gas reactions proceeding from the sheet steel.

The base enamels which are viscous and hard at the stoving temperature are described as filling bases, while low viscosity, soft frits which wet readily and are capable of dissolving iron oxides are known as network base enamels. The proportions in which they are mixed and the amount of quartz added depend on the quality of the steel and the thickness of the steel sheet as well as on the stoving temperature and the dwell time. Here again, the proportion of frits and the additives used for the milling process are selected empirically and either accepted or varied under practical conditions. Predictions as to the optimum properties such as compatibility of the frits with one another, bonding to differently cast qualities of steel and flow properties of the slips were rarely possible.

What Is Porcelain Enamel Cookware?

Porcelain enamel cookware refers to pots and pans made of metal that’s coated with a form of glass called porcelain enamel, which is bonded to the iron, steel, stainless steel or aluminum metal to form the body of the cookware. Porcelain enamel cookware from a host of manufacturers offers a huge variety of solid colors and designs on an easy-to-clean surface.

Quality Differences

Porcelain enamel provides a hard, lustrous finish that won’t scratch, corrode, fade or peel with normal use. However, it may chip or crack if the utensil is dropped on a hard surface. Most porcelain enamel cookware has an outside enamel coating, with teflon or plain metal on the inside. It comes in a wide range of prices. Price differences are based on metal thickness, number of porcelain enamel coats, color and design, and accessories such as covers and high-temperature plastics for handles. Better grades of porcelain enamel cookware have seamless coatings.

Enamelware

Enamelware is a variety of porcelain enamel cookware that’s distinguished by having a porcelain enamel coating on the inside as well as the outside. Enamelware has a base of steel, stainless steel or cast iron. The porcelain coating is applied after the utensil is formed to create a smooth, non-porous surface inside and out. Enamelware isn’t affected by heat, humidity or food acids and can be used to cook, bake or roast foods, or as a serving or storage utensil. Cheap enamelware can scratch or chip easily; high-quality ware has a thicker enamel coating that resists scratches and chips.

Cookware Cautions

Porcelain enamel cookware is very strong and durable, with excellent heat-transfer characteristics. It doesn’t react with acidic foods like tomatoes, and you can use any type of metal or plastic cooking utensils. But there are some things you shouldn’t do with this cookware. For instance, you shouldn’t use it over high heat for extended time periods. Extreme high temperatures can melt the porcelain enamel coating. And you shouldn’t allow porcelain enamel cookware to boil dry, especially on a glass or ceramic cooktop. This can crack the finish.

Cleaning Porcelain Enamel

Porcelain enamel is quick and easy to clean. This cookware is stick-resistant, and resists staining and scratching. Clean your cookware while it’s still warm; don’t let it sit around until food residue dries and hardens. Use a dish sponge or a plastic or nylon dish scrubber. Don’t use steel wool soap pads or abrasive household cleaners as these can scratch the finish over time. Alternatively, you can put porcelain enamel cookware in a dishwasher after wiping out any food residue.

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