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.
Enamel is also used by artists and in jewellery, famously in Russia’s Fabergé eggs. Decorative enamelling was the first use of the process of enamelling, dating back to the 13th century BC. This type of enamel is usually applied to copper and its alloys and to gold and silver. We make Vitreous Enamel by smelting naturally occurring minerals, such as sand, feldspar, borax, soda ash, and sodium fluoride at temperatures between 1200 °C and 1350 °C until all of the raw materials have dissolved. Other metallic mineral may be added to give specific properties or colour. The molten glass which is formed is either quenched into water or through water-cooled rollers. This rapid cooling prevents crystallisation and is said to be in a metastable state. This material is called “frit”. To make a usable enamel the frit will be ground in a rotating ball mill either to produce a water-based slurry or a powder. Clays are used in the water-based products to give a product which can be applied to the metal by spraying, dipping or painting by brush. At the milling stage, other minerals will be added to give the properties which are required of the final enamel. Colour is introduced by the use of metal compounds. The recognisable blue enamel is produced using cobalt. Powdered enamels are applied by dusting or using electrostatic equipment. The final glassy finish so typical of vitreous enamel is produced by firing in furnaces at temperatures up to 900 °C. As it cools, it fuses to give glass-coated metal. This ‘firing’ process gives vitreous enamel its unique combination of properties. The smooth glass-like surface is hard; it is scratch, chemical and fire resistant. It is easy to clean and hygienic. It all started 3500 years ago in Cyprus. Since 1500 BC, enamelling has been a wonderful, durable, attractive and reliable material. You will recognise it as the material used to produce the now highly collectable advertising signs produced during the early 20th Century.
The ‘Hovis’ and ‘Virol’ signs were part of the everyday street scene. Your cooker will almost certainly have a vitreous enamelled oven and the higher quality cookers will use it on the outer parts. Your cast iron or steel bath will have been vitreous enamelled. Less obvious are the storage silos on farms, usually blue or green; they tower over the surrounding countryside. Carl Faberge used enamel for his unique eggs and jewellery and the Battersea enamellers are famous for their copper enamelled boxes. These are only two of the better-known groups of highly skilled artists who used this very special material. Vitreous enamel can be applied to most metals. For jewellery and decorative items it is often applied to gold, silver, copper and bronze. For the more common uses, it is applied to steel or cast iron. There are some specialised uses on stainless steel and aluminium.
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.
Graffiti can be easily removed from vitreous enamel – click Case Study Cleaning of graffiti“
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). The picture is of some Ming dynasty enamel from the 16th century. 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.