Diamonds in vintage jewelry

Diamond is a crystalline form of pure carbon, formed under extreme heat and pressure deep in the earth. At 10 on the Mohs scale it is the hardest natural material known, roughly an order of magnitude harder than the next hardest common gem, corundum, which is why a diamond is the one stone that can scratch every other stone in a piece of jewelry, including another diamond.

That extreme hardness is also why diamond withstands a century of daily wear better than any other gem, but it is worth remembering that hardness is resistance to scratching, not resistance to a sharp blow. Diamond has a cleavage plane and can chip at the girdle or culet if struck directly at the wrong angle, which is why old stones sometimes show small girdle chips.

Rose cut diamonds have a flat, unfaceted back and a domed top covered in triangular facets, usually between three and twenty-four of them. They were the dominant cut through the Georgian period and into the Victorian era, prized for a soft, glinting light rather than fire, and they remain popular today for their romantic, almost candlelit look.

Old mine cut diamonds followed, cushion-shaped with a high crown, a small table and a large culet, cut from the rough with less concern for maximizing weight retention than modern cutting allows. Old European cut diamonds refined this into a rounder, more symmetrical outline through the late Victorian, Edwardian and Art Deco periods, while transitional cuts from the 1930s and 40s begin adopting the wider table and lower crown that would become standard by mid-century.

Old cut diamonds were faceted by hand to preserve as much weight from the rough as possible, so it is common to see slightly irregular facet junctions and a culet that is visible to the naked eye, none of which is a flaw so much as a fingerprint of the period. Inclusions typical of natural diamond, such as small crystals, feathers and clouds, appear across all periods and cut types.

Because the pavilion and culet of a mounted stone are often partly obscured by the setting, a clarity assessment made in place is necessarily an estimate rather than a laboratory-grade reading. A careful seller states this plainly rather than quoting a precise clarity grade for a stone that has not been examined loose.

The great majority of diamonds in antique jewelry are untreated. Two treatments do appear in the wider market and are worth knowing: laser drilling, which bores a fine channel to a dark inclusion to lighten or remove it, and fracture filling, which fills a surface-reaching break with a glass-like substance to make it less visible. Both are detectable by a gemologist under magnification and both must be disclosed.

High pressure high temperature treatment, used to alter the color of certain diamonds, and treatments to induce artificial color, are modern processes generally associated with more recently cut stones rather than antique material, but any seller should confirm a stone's treatment status as part of a proper description rather than leaving it assumed.

Weight is estimated from the stone's measured diameter and depth using standard formulas for its cut type, and any reputable description should state clearly that the weight is estimated rather than taken from a certificate. Color is judged face-up, against a neutral background and under controlled lighting, which is less precise than the loose-stone, table-down grading used for laboratory reports, so expect a stated range, such as J to K, rather than a single confident letter.

Removing a diamond from a period setting to send it for laboratory grading carries real risk: prongs can be damaged, delicate galleries can crack, and a hand-finished antique mount is not always easy to reset cleanly afterward. For that reason, most dealers grade antique diamonds in place and disclose that the figures are estimates, reserving formal certification for stones that are already loose or for pieces where a customer specifically requests and pays for the extraction and grading.

Diamond's hardness makes it the most forgiving stone in the jewelry box for everyday wear, and it is one of the few gems that generally tolerates gentle ultrasonic cleaning, provided the setting itself is sound and there are no other, more delicate stones sharing the piece.

The real risk to an antique diamond is not the stone but the mount around it. Prongs wear thin over decades, and a loose setting can let even the hardest stone fall out and be lost. We check every claw and setting on a diamond piece before it is listed, and we recommend an annual check for any antique diamond ring worn daily.

Paste, a lead glass historically used to imitate diamond, appears throughout Georgian and Victorian jewelry, often foiled at the back to increase brilliance, and it is soft and easily scratched compared to a real stone. Modern simulants such as cubic zirconia and moissanite are harder and more convincing, though a gemologist distinguishes them readily from genuine diamond using thermal, optical and refractive tests.

A diamond simulant in a period piece is not automatically a problem, since paste jewelry was made and sold honestly as paste at the time, but the description you are given should state plainly whether a stone is diamond, a historic paste, or a later simulant, rather than leaving the word diamond to imply more than it should.