Extract from S. Rossi, “Enamel and design. The potential of enamelled materials”, Fausto Lupetti Editore, 2011
I don’t fade
When we have an artefact and we grow attached to it, we want it to retain his initial appearance. Many materials, however, suffer from environmental interaction showing oxidation or surface changing. Considering a plastic object or a painted surface, often when exposed to solar radiation they show a colour change: fading, yellowing, chalking. The colour tends to lose its glossy appearance and brightness, showing signs of age. This phenomenon is due to the interaction of radiation, particularly ultraviolet, on bonds of organic substances. Anti-UV additives are often added in polymers and organic coatings to limit this phenomenon, but often it is not a simple operation. Considering the enamel, both the matrix and the pigments responsible of the colour, are oxides and inorganic compounds that are not affected, given the greater strength of chemical bonding, by the ultraviolet radiation degradation. To evaluate the colour stability, coatings are often subjected to UV radiation exposure (ASTM G154) assessing the change of gloss and colour (Figure 1). Figure 2 and Figure 3 show two painted panels, respectively powder painted and enamelled, subjected to 500 hours of UV-B radiation, maintaining a part of the sample shielded from radiation. It is evident that the enamelled sample shows an unchanged surface, unlike the painted surface that exhibit a significant change in the colour.
We can therefore say that one of the great advantages of the enamel is the inalterability of colour, which remain bright and unchanged over time. This aspect is crucial and make enamel one of the best coatings for outdoor use.
Exposition of porcelain enamel and paint to UV-rays.
Below: Results of the exposition to UV-rays: enamel (on the left) shows no change between the exposed and the non-exposed parts, while the color of paint (on the right) has faded upon exposition to the UV-rays.