There are no fixed properties for enamels as their composition and use is so varied.
The application of enamel may be purely for aesthetic reasons, functional purposes or both.
The following properties are considered of importance, depending on the application and product/process types.
Enamels are normally required to be in compression in the fired state to avoid the fault of crazing. Expansion is controlled by the composition of the fired enamel on the metal.
The colours available will depend upon the firing temperature, the chemistry of the enamel, and the composition of the chosen colour addition.
Depending on the application, chemical and physical durability may be of importance. Various tests are employed for the different product types to assess durability.
Enamels must mature within an appropriate temperature and time interval. There must also be a suitable range over which maturity is reached in order to allow for process variables.
They are applied by spraying and dipping, or by dry dusting or electrostatic methods. In some cases, enamels are applied in single layers or, in order to obtain suitable finishes and improve adhesion on certain metals, in two layers, a base coat and a topcoat. Certain pre-treatments of the metal such as ‘pickling’ in acid baths to remove grease, and pre-oxidation to create an oxide bonding layer may be required.
Enamels are usually fired between 700°C and 1000°C depending on their composition, the substrate metal and the length of time in heating.