Stella Layton, Chief Executive and Assay Master of the Assay Office Birmingham (AOB), spoke about diamond grading at CMJ’s UK Jewellery Conference last month: “It’s inconsistent – it’s based on subjectivity and there is a wide range of grading happening globally across diamonds, not just lab to lab but person to person.” Layton said that there is as yet no science that may be applied across the board to determine the exact grade of a stone, and even standard guides used to unify graders are open to interpretation. The lack of objective grading standards leaves the industry vulnerable to less credible labs producing over-generous reports that are not true to a stone’s actual worth. "So how did the industry get itself into this predicament in the first place?", asks Stacey Hailes of Professional Jeweller.
In 1955, she writes, the Gemmological Institute of America (GIA) issued its first diamond grading report, which would come to be accepted as the international standard for diamond grading. GIA was at the fore of diamond grading, but soon other labs set up their own grading services, each devising their own methods. Questions arose about how their grades compared to the GIA’s. In response, labs devised a chart comparing their grading standards to GIA's, and many adopted GIA terminology, but without the GIA standards. London Diamond Bourse president Harry Levy says that this led to a downfall of diamond grading. “To attract business, some of these labs began to soft grade,” explains Levy. “If a stone was a borderline colour, say on the border of G and H they would give it a G, and similarly for clarity. This attracted clients as they thought they were getting a better grade than from a GIA lab. This whole methodology was abused", and now the notion of overgrading is well established.
The issues are not new, but have become particularly pertinent with the rise of online diamond sales and the development of new technologies to treat and improve diamonds. Overgrading, or simply grading inconsistency, has huge potential to hurt consumer confidence in diamonds. Indeed, unreliable grading effects the whole industry and leaves retailers in a conundrum: is it sensible to compete with less reputable retailers at the expense of consumer trust? At least one things is clear; everyone seems to agree with the sentiment of White Pine UK head of valuation Marie Chalmers when she says that, "We need to regulate diamond grading labs worldwide and stop trading with laboratories we know are not telling the truth.”