Vitreous enamel information

This section contains information and useful links about vitreous enamel.

See also:

Frequently asked questions (also relating to care of enamel in common applications)

A short history of enamel

Useful links

 

WHAT IS VITREOUS ENAMEL?

  • Enamel or vitreous enamel is really a thin layer of glass fused by heat on to the surface of a metal.
  • Enamel is part of everyday life and found all around us. It covers many kitchen surfaces including cookers, saucepans and washing machine drums. You will find enamel covering cast iron or steel baths and clock and watch faces. Enamel is also used by artists and in jewellery, famously in Russia's Fabergé eggs.
  • Out of doors, we use enamel for street signs, Underground station signs, architectural panels, storage tanks and in lots of other places. It is selected because it is weatherproof, vandal resistant, fire proof and because it lasts and lasts and lasts. The Titanic's Captain Smith's bathtub enamel has survived very well under the sea.
  • We make enamel by melting tiny coloured glass particles on to red-hot metal in 800 degrees C furnaces. As it cools it fuses to give glass-coated metal. It all started 3500 years ago in Cyprus. Since 1500 BC enamelling has provided a wonderful, durable, attractive and reliable material.

APPLICATIONS AND PROCESS

You will recognise vitreous enamel 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 just two of the better known groups of highly skilled artists who used this very special material.

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

The glass will be applied to the metal by a various methods either as a powder or mixed with water. This is followed by heating in a furnace to a temperature usually between 750 and 850 degrees Celsius. 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.

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 become shabby. 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 (see our page on Enamelling History). If you want something where the colour will never fade – use vitreous enamel.

Following 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.

EEA GUIDELINE 1001 FOR TESTING ENAMEL FOR FOOD CONTACT COMPLIANCE

The members of the technical committee of EEA have agreed the first guideline of EEA (testing method for food contact compliance). This EEA guideline has the reference number 1001 and is available on the EEA website.

COMPARISON OF THE PROPERTIES OF VITREOUS ENAMEL V EPOXY PAINT

 

Vitreous
Enamel

Epoxy
Paint

 

Titania
white covercoat

 

 

 

 

ACID RESISTANCE

Class AA

Class AA

Cold acid ISO 2722

 

 

 

 

 

ACID RESISTANCE

Weight Loss 2g / Sq metre

Weight loss 2g / sq metre

Hot acid ISO 2742

 

 

 

 

 

CAUSTIC SODA RESISTANCE

Weight Loss 9g / Sq metre

Weight loss 45g / sq metre

ISO 2745

 

 

 

 

 

COMBUSTION

WILL NOT IGNITE OR BURN

500 C

 

 

 

THERMAL RESISTANCE

OK to 500 C

Visible yellowing above 320 C

 

 

 

SOFTENING POINT

~540 C

80-100 C

 

 

 

BONDING

FORMS STRONG CHEMICAL

NO CHEMICAL BONDING

 

BOND WITH SUBSTRATE

 

 

 

 

CURING TEMPERATURE

TYPICALLY 800-840 C

TYPICALLY 200 C

 

 

 

GRAFFITI RESISTANCE

YES

NO

 

 

 

UV RESISTANCE

NO YELLOWING

POTENTIAL COLOUR CHANGE

 

 

 

LIFE TO FIRST MAINTAINANCE

20+ YEARS

4-5 YEARS

 

 

 

SCRATCH HARDNESS EN15771

Mohs 5

Mohs 1

 

 

 

TETRA-SODIUM PYROPHOSPHATE

 

 

BS EN ISO 28706-3:2011

Weight Loss 0.8g/Sq Metre

Weight Loss 0.9g/Sq Metre

 

 

 

PENCIL HARDNESS *

>9H

2H

 

 

 

Pencil
hardness scale (where 6B is the softest and 9H the hardest)

6B-5B-4B-3B-2B-B-HB-F-H-2H-3H-4H-5H-6H-7H-8H-9H