A Beginner's Guide to Buying Vintage Onyx Jewellery

Why Vintage Onyx Still Turns Heads

Onyx has been set into jewellery for thousands of years, from Roman signet rings to the black-dominant designs of the Art Deco period and the mourning jewellery of the Victorians. Its appeal hasn't faded: that deep, glossy black flatters almost every skin tone, works with both gold and silver, and never really looks dated. Because it has been so consistently popular, there's a healthy supply of pre-owned pieces about — brooches, rings, cufflinks, pendants and cameo-style carvings — at prices that often beat anything new of comparable quality.

The catch is that age brings complications. Clasps get replaced, settings wear, stones are swapped or glued back in by well-meaning owners. Before you hand over your money at a market or an antique shop, three checks matter more than any other: clasps, hallmarks and stone condition.

Know Your Black Stones: Onyx, Jet, Glass and Dyed Agate

True onyx is a form of chalcedony, a cryptocrystalline quartz sitting at around 6.5 to 7 on the Mohs scale. Natural onyx is banded, so the solid black material used in most jewellery is actually dyed agate or dyed chalcedony — and has been for well over a century. Dyed doesn't automatically mean fake or modern; it means you should know what you're looking at.

• Jet — fossilised wood, not stone at all. Noticeably lighter in the hand, warm to the touch, and it leaves a brown streak. Whitby jet is frequently sold as onyx by mistake.
• Black glass — often called "French jet". Cold like stone, but lighter, and a loupe will usually reveal tiny bubbles.
• Sardonyx — banded brown, red and white chalcedony, the traditional material for cameos. The coloured layers are carved to create the portrait.
• Resin and plastic — warm to the touch, very light, and a fingernail will scratch it.

A ten-pound jeweller's loupe is the single best investment a beginner can make.

Inspect the Stone Before You Fall in Love

On affordable vintage pieces, stone condition drives value more than anything else. Work through this list slowly, in daylight rather than under a market lamp.

• Chips and nicks along facet edges and corners. Onyx is tough but brittle, and a chipped corner is permanent.
• Cracks and crazing — fine internal lines, sometimes caused by heat or the dyeing process. Hold the piece up to a lamp to check.
• Loose stones — press gently with a fingernail. Any movement means claws or a bezel need attention.
• Glue and resin — a cloudy rim or brownish film around the stone usually points to a DIY repair.
• Backs and undersides — a painted or foil backing can be used to fake depth of colour.

Clasps, Fittings and Hidden Repairs

Clasps are the hardest-working part of any piece and the most frequently replaced. On a bracelet, a tired clasp is a lost bracelet.

• Bolt rings — open and close it. The spring should snap back firmly. Grittiness or a weak return is a warning sign.
• Barrel and box clasps — the tongue should engage with a definite click and the halves should meet flush. Look for bent or filed tabs.
• Safety chains and figure-of-eight catches — a mark of quality, and worth having added to anything you plan to wear regularly.
• Metal matching — a yellow replacement clasp on white metal suggests a repair. Not a dealbreaker, but it should be reflected in the price.
• Brooch pins and hinges — check for solder blobs, replaced pin stems and a catch that holds under a gentle pull.

Hallmarks, Metals and What They Tell You

In the UK, gold and silver items over certain weights must be hallmarked. Look for the maker's or sponsor's mark, the assay office symbol and a fineness mark: 375 for 9ct, 585 for 14ct, 750 for 18ct and 925 for sterling silver. Before 1973 you'll usually also find a date letter, which is the quickest way to pin down a year. A small hallmark reference book or a jeweller's opinion will decode it in seconds.

Be wary of stamps reading "9ct gold front", "rolled gold", "gold filled" or "plated". These describe a layer of gold over a base metal — perfectly wearable, but they should not be priced as solid gold. Unmarked pieces do exist, especially imports, but if a seller insists something is 18ct with no mark to show for it, factor that uncertainty into what you pay. Greenish staining on the skin or a reddish gleam at wear points often means the plating has worn through.

Buying Wisely and Looking After Your Piece

At markets, ask the questions a good dealer expects: How old is it? Has anything been replaced? Is the stone original to the setting? Will you take it back if my jeweller disagrees with your description? Reputable antique dealers offer a returns period and an honest written description, and that is worth paying a little more for. Take a loupe, and remember that a magnet will not attract gold or silver but may reveal a base metal pin.

Once the piece is yours, keep onyx away from ultrasonic cleaners, steam cleaners and household chemicals, all of which can dull a polished surface or loosen a setting. Wipe it with a soft dry cloth, store pieces separately so harder stones don't scratch softer ones, and have claws and clasps checked every year or two if you wear the piece often. A well-cared-for onyx brooch or ring will comfortably outlast all of us — which is rather the point of buying vintage in the first place.