Coating is a thin film, paint or ink on the surface of a gem that changes its color or look.
In more detail
On a diamond, a very thin layer can mask the body color. Coatings can scratch and wear off, and once a gemologist suspects one, it is easy to identify. GIA treats coating as unstable and issues no grading report for a coated diamond. A coated stone cannot be called padparadscha.
On a grading report
Labs state the coating. For a coated diamond, GIA issues an Identification Report instead of a grading report.
Related terms
- Color treatment: A color treatment is any process that changes a diamond's color, such as HPHT processing or coating.
- Fracture filling: Fracture filling is a clarity treatment that injects a glass-like filler into a crack to make it less visible.
- Identification Report: An Identification Report states what a material is, without color or clarity grades. GIA issues one for simulants and for diamonds with unstable treatments, such as coating or fracture filling.
- Treatment: A treatment is any process, other than cutting and polishing, that changes a gem's color or apparent clarity. Anyone who sells a treated gem must disclose the treatment.
- Disclosure: Disclosure is telling the buyer, before the sale, that a gem is treated, laboratory-grown or an imitation.
- Padparadscha: Padparadscha is a sapphire of soft pinkish orange to orangey pink. Its tones are pastel and its saturation low to medium.