Enamelling is said to date back to ancient Greece and has been used for centuries to protect a variety of materials. An enameller is someone who applies enamels to surfaces so as to decorate and protect them. These can range from general household items such as radiators, as the enamel will not be damaged by the heat, to bathroom surfaces, such a bath tubs, where decoration as well as protection are both key to its requirements. The basic enamelling process is common to all materials, although there are slight variations according to what type of enamel is used or whether the material has already been moulded.
When would I need an enameller?
Enamel can be applied to a surface to protect it and harden it so that its working life can be greatly extended. It also helps prevent any damage that may be created though wear and tear, or from products which will be used on it. Cast iron baths are a great example of this. They can last for decades if they are covered in enamel as it protects them from cleaning products, and hardens their surface thus makes them easier to keep. Enamellers are also vital for AGA and Rayburn production, as a vitreous enamel surface is essential for their surfaces.
What is enamel?
To help understand when enamel needs to be used, a definition of its properties needs to be given. The term enamel can be applied to a number of different products. Enamel paint is applied to radiators, as normal paint will not stick to its surface, which is enamel. It is also strong enough to withstand the heat which a radiator produces, unlike other finishes. Enamels can also be used on ceramics, glass and metals and can be decorative or merely serve as a protector. The finish which enamel produces is usually a hard and glossy surface. It is produced by crushing glass to a powder that is finer than sugar and then heated at an extremely high temperature to make it into a liquid. To produce different colours, various transition metal elements are added to the glass mixture, or marble chips or dust can be added to produce a marble effect.
The enamelling process
The enamelling process depends on the material which is to be enamelled. The method usually only takes a few hours, including the drying and firing procedures.
- For metal surfaces which have already been shaped, such as a cast iron bath, the metal must be clean before it is enamelled. This is done by blasting the surface of the metal with chilled iron grit through nozzles using compressed air, or by using a particular machine which uses centrifugal force. This removes any dust or sand particles which may be attached to the metal and which will interfere with the enamel sticking properly.
- Sheet metal also needs to be degreased using two chemical cleaners; firstly an organic solvent and then an alkaline solution.
- Acid pickling, using hydrochloric or sulphuric acid, de-scales the surface allowing a stronger bond between the metal and the enamel to occur. The metal is then rinsed in running water.
- After this a nickel dip, which is a mixture of nickel sulphate and boric acid, is sometimes used to coat the metal in a layer of nickel so as to help form a better bond with the enamel. The metal is then dipped in a neutralizer solution to remove any traces of acid and to help prevent rusting.
- The enamel then needs to be prepared. The raw materials are weighed carefully and then melted in batches in a furnace. This is then run out of the furnace in a thin stream into a tank of cold water, producing small fragments.
- Before this is applied to the surface it is ground down into a powder using a mill which uses blocks of enamel as its grinders. If the enamel is to be applied wet, this ground down substance is mixed with clay and water to make a slurry-like substance.
- If the enamel is to be applied dry, the surface it is being applied to is heated to a temperature which is higher than the melting point of the enamel and then the enamel is dusted onto its surface. The metal is then heated using cabinet or conveyor driers and then fired in a furnace to make a tough, smooth and glossy ceramic style exterior.
- Wet enamel is applied by dipping the metal in a large tank of the enamel, or it is sprayed onto the surface of the metal. It is then left to drain and a thin coating of the enamel is left. The metal is also heated and fired in a furnace as with the dry enamel.