Extract from S. Rossi, “Enamel and design. The potential of enamelled materials“, Fausto Lupetti Editore, 2011
I don’t get wet!
Among the advantages of the enamel there is certainly the ease of cleaning and the possibility of having a non-stick coating. These properties have led the enamel to be a valid alternative to PTFE, commercially called Teflon®. The wettability of the surface enamel then becomes a key feature for applications where these characteristics are required. To quantify the wetting phenomenon, the so-called contact angle is measured, considering the shape of a liquid drop deposited on the examined surface: the droplet spreads over a surface with high surface energy; on the contrary, it tends to form a more or less pronounced ball on a surface with lower surface energy. The “cleanability” of a surface, related to its wettability, is influenced by many factors such as the type and extent of the forces acting on the contact surface, the presence of additives that promote adhesion, the surface geometry, its roughness , the intermingling of materials in contact with the enamel, the hardness and chemical resistance of the surface. With an enamel of suitable composition can be obtained very smooth surface, low roughness, with a few anchor points and then adhesion, spreading and very resistant to penetration of aggressive and attack by chemical agents. It follows that this coating has a high durability, remaining unchanged over time, without colour change or gloss loss.
Test of wettability for enamel.
If I get dirty. I clean myself!
Observing our cities we can take notice of the amount of object and structures aesthetically damaged by graffiti and tags. The council and transport administrations spend thousands of Euros for cleaning the spoiled surfaces. The soiled buildings facades can only be repainted. Painted metal surfaces like walls, street furniture or public transport’s stops are difficult to repaint because the surface preparation step, required for a fine end result, could be complicated.
The step taken against scribbles and drawings, given that spray paints are organic compounds, is often the employment of organic solvents. Unfortunately, paints are also organic by nature, and they are therefore frequently faded while trying to remove the scribble; the surface becomes opaque and an unpleasant halo forms. There are two main ways to get rid of this problem. The first one is to reduce the wettability of spray paints on surfaces, the second to find a solvent able to remove graffiti and keep the surface unchanged.
One of the best solutions can be found in enamel. Enamel shows actually a low surface wettability (as will be said in next chapter) that hinders the attaching of the spray paint. Moreover, thank to its vitreous nature, enamel resists to every organic solvent and graffiti can be easily removed. As we can see in the reported images, where an enamelled surface (left) is compared to a painted one (powder coated, right), the writing is easily removed from the enamelled surface while it lasts on the painted one.
Enamelled surfaces resist also to acids (except Hydrofluoric acid) and to all disinfectants. This aspect is very important, as we will see in other chapters, for the use of enamel in public environments and places.
Test of cleanability for enamel.