Ion plating, also referred to as physical vapour deposition or PVD, is a vacuum-deposition coating technique in which a metal or metal-compound coating is applied to a substrate by vapourising the source material and ionising it before deposition. In jewellery and watch manufacture, ion plating produces hard, durable and chemically stable surface coatings in colours that are difficult to achieve with conventional electroplating.

Process

The substrate is placed in a vacuum chamber, the air is evacuated, and a target of the source material is heated or sputtered to produce a vapour. An electrical bias accelerates the ionised vapour towards the substrate, where it deposits as a thin film typically a few microns thick. Common coating materials include titanium nitride (golden colour), zirconium nitride (paler gold), titanium carbonitride (dark grey to black) and chromium nitride (silvery). The resulting coating is hard, generally rated above 1,500 Vickers, and bonds tightly to the substrate.

Application to jewellery

Ion plating is used on stainless-steel and titanium watch cases, bracelet links and bezels, and on jewellery in base metals or sterling silver where a coloured surface is wanted that resists wear better than electroplated gold. Black PVD coatings, in particular, have become widespread in fashion-forward men's watches and jewellery. The bond between the coating and the substrate is significantly more durable than electroplating, but the coating remains a surface layer and can wear through over many years of heavy use, particularly at high-contact areas.