Plating and patinae

The word "patina," in everyday language, covers a wide range of phenomena most often related to changes in the surface of objects due to the effects of time, the environment, or surface treatments.

Their semantic commonality is the modification of the appearance of objects, particularly their color.

Their scientific commonality can be considered as the existence, on the surface of objects, of a layer or deposit of color (or texture) different from that of the "bare" material.

We talk about weathered stone, weathered plaster, even weathered paint, and, of course, weathered metal. The origin of these surface changes can be unintentional or intentional. The former generally results from the action of the environment over varying periods of time, while the latter belongs to the category of surface treatments.

With regard to metal objects, which are the only ones considered here, patinas are defined as the formation on the surface of compounds resulting from chemical reactions between the material and the external environment, whether these reactions are a consequence of the action of a natural environment, in which case they are referred to as corrosion patinas or natural patinas, or whether they have been intentionally applied during surface treatment, in which case they are referred to as intentional patinas.

With regard to natural patinas, a further distinction is sometimes made between so-called "noble" patinas, which preserve the original form of the object, and so-called "base" patinas, which are in fact a more or less regular accumulation of corrosion products in the process of evolving. It seems more accurate to refer to protective patinas and non-protective corrosion.

Prized by art lovers, patina, a term that only appeared in the 17th century and was not applied to metal until the following century, is also often considered a guarantee of authenticity. It is therefore not surprising that, very early on, artificial patinas were developed to imitate natural patina.

The two effects can combine, either intentionally or unintentionally: some intentional patinas are obtained through a combination of chemical surface treatment and exposure to a natural environment; conversely, the existence of an intentional patina on certain archaeological objects, for example, can be masked by subsequent deterioration.

In addition, certain corrosion patinas are deliberately obtained by choosing a material that, through exposure to the natural environment, undergoes a desired change in appearance and...