Gold standards through the ages: from Georgian glow to modern marks (now with the key dates collectors love)

Gold has its own grammar. Those tiny stamps inside a ring—or the numbers on a clasp—tell you how pure the gold is, where it was tested, and often when your jewel was made. Here’s a Parkin & Gerrish guide to gold standards from the Georgian era to today—now woven together with the most-asked extras: why some antique rings carry no hallmark, the legal milestones, why Chester marks are catnip for collectors, the practical mixing of carats within a single jewel, and a quick note on platinum stamps like IRID. PLAT.

Carats vs parts-per-thousand (what the numbers mean)

Gold purity is expressed two ways:

• Carat (ct / K) — out of 24 parts

  • 9ct = 9/24 ≈ 37.5%

  • 12ct = 50.0%

  • 14ct ≈ 58.5%

  • 15ct = 62.5%

  • 18ct = 75.0%

  • 22ct ≈ 91.6%

  • 24ct ≈ 99.9% (theoretical “pure”)

• Fineness (‰) — parts of pure gold in 1000

  • 375 (9ct), 500 (12ct), 585 (14ct), 625 (15ct), 750 (18ct), 916 (22ct), 990/999 (24ct)

Modern British and European marks most often show the fineness number (e.g. 750 for 18ct).

Why 24ct isn’t practical for daily jewellery: pure gold is very soft. Rings and claw settings would bend, creep and loosen. Most everyday pieces use alloys (gold plus copper/silver/palladium, etc.) for strength, spring and colour.

A timeline of UK/Irish standards (Georgian → today)

• Georgian (1714–1837)
  22ct and 18ct dominate finer work; lower-carat alloys appear for practical components (backs, shanks, pins).

• 1784–1890
  Duty mark (sovereign’s head) paid on gold/silver; sending work to assay cost time and money, which helps explain some unmarked period pieces. Duty abolished 1890.

• 1854
  UK legalises new carats 9ct, 12ct and 15ct (alongside 18ct and 22ct). This is why you see so much 12ct & 15ct in late-Victorian/Edwardian jewels.

• 1932
  12ct and 15ct discontinued; 14ct (585) adopted in line with international standards. If you see a clear 15ct/625 or 12ct/500, it’s a pre-1932 clue.

• Hallmarking Act 1973 (effective 1975)
  Modern UK hallmarking framework; platinum formally hallmarked; fineness numbers standardised (e.g., 375/585/750/916).

• Chester Assay Office closed 1962
  The famous three wheatsheaves with a sword town mark stops that year—hence highly collectible.

Mixed carats in one jewel (very normal—by design)

Historic workshops often combined carats to balance beauty, strength and cost:

• Shanks & backs: commonly 9ct, 12ct or 15ct for hardness and spring (these take the knocks).

• Tops & settings: frequently 15ct or 18ct for colour and fine work (what you see).

• Pin stems: stickpins and brooch pins were often 9ct (or tempered steel), with a 15/18ct decorative head.

• Georgian diamond work: silver-topped fronts (to flatter diamonds by candlelight), gold-backed—and a lower-carat gold shank or back for strength.

This isn’t corner-cutting; it’s good engineering.

12ct & 15ct: why we love them (and what they tell you)

12ct (500‰) — the sturdy sweetheart

• Legalised: 1854

• Typical uses: late-Victorian lockets, guard/Albert chains, photo pendants, brooch backs

• Colour: soft, buttery yellow—perfect “daywear” tone

• Discontinued: 1932 → replaced by 14ct (585)

15ct (625‰) — the connoisseur’s clue

• Legalised: 1854

• Beloved for: workability (granulation, fine wire, millegrain), and a glowing hue that flatters turquoise, seed pearls, garnets, opals

• Where seen: fancy link chains, five-stone half hoops, navette rings, tremblant sprays, and decorative pin heads

• Discontinued: 1932—so a crisp 15ct hallmark screams pre-1932

Why an antique ring might have no hallmark (even when it’s excellent)

• Pre-standard alloys: Before 1854, 9/12/15ct weren’t legal UK standards. Superb late-Georgian/early-Victorian rings can be unhallmarked.

• Duty & cost: From 1784–1890 gold carried a tax; assay/hallmarking cost time and money. Not every workshop sent every component.

• Wear & tear: Inside-shank marks can polish away after a century on the hand.

• Exemptions & tiny parts: Some small items historically exempt; little parts (pin stems, jump rings) often unstamped.

• Re-shanks & conversions: Later resizing or new shanks can remove original marks.

• Foreign/continental pieces: May show numeric fineness (375/585/750/916) or local symbols rather than British devices.

What to do: Read the jewel as a whole—construction, stones, settings—and test the metal (acid/XRF). A faint or absent hallmark doesn’t doom authenticity.

Where to find the marks

• Rings: inside the shank (often opposite the setting)

• Chains: T-bars, dog clips, clasp tongues, tiny end-ring tags

• Pendants: the bale and back edge

• Brooches: reverse plate (sometimes under the pin)

• Stickpins/tie pins: usually on the head, not the stem

UK & Ireland at a glance

• Town marks: London (leopard’s head), Birmingham (anchor), Sheffield (rose), Edinburgh (castle), Chester (wheatsheaves + sword, closed 1962), Dublin (harp + Hibernia).

• Fineness: 375 / 500 / 585 / 625 / 750 / 916 on gold; date letters indicate the assay year; sponsor’s (maker’s) mark identifies the workshop.

• Duty head: on gold/silver 1784–1890.

USA, France & friends

• USA: No state assay office; you’ll see 10K/14K/18K with a maker’s trademark (9ct isn’t legally “gold” in the US, though it is in the UK). You’ll also meet GF (gold-filled), GP (gold-plated), HGE (heavy gold electroplate).

• France: Since 1838, eagle’s head punch for 18ct; owl for imported gold. Stamps are tiny and often placed on the outside of a ring’s shank or the bale edge.

• Portugal: Traditionally loves 19.2ct (exactly 800‰)—the famed rich “Portuguese gold.”

• Continental Europe: Numeric fineness (375/585/750/916/999) plus national control marks; many states also use a Common Control Mark for cross-border recognition.

Platinum notes (and that IRID. PLAT. stamp)

• UK: Platinum hallmarking was formalised with the 1973 Act; full British platinum hallmarks appear from 1975 (today typically 950). Earlier British platinum may be simply PLAT/PLATINUM or unmarked.

• USA: Early 20th-century American platinum is often stamped “IRID. PLAT.” or “90% PLAT 10% IRID”—a platinum–iridium alloy used widely in Edwardian–Art Deco settings for added hardness. Later you’ll also see PLAT or .950.

In praise of 9ct (yes, really)

9ct (375) is wonderfully tough, often more scratch-resistant, and historically right for late-Victorian/Edwardian daywear. It’s ideal for shanks, backs and everyday chains—and lets you invest in what matters most: design, workmanship and condition.

Quick date anchors 

• 1784–1890 — Duty mark on UK gold/silver (sovereign’s head)

• 1854 — UK adds 9ct, 12ct, 15ct (alongside 18/22)

• 1932 — 12ct & 15ct abolished; 14ct adopted

• 1962 — Chester Assay Office closes

• 1973/75 — Modern UK hallmarking; platinum fully hallmarked

Final word from us

A 15ct face with a 9ct shank, a 12ct locket on a stout Victorian chain, a Chester-marked keeper ring—these details aren’t quirks; they’re clues. They tell you how a jewel was made to be worn and loved. If you’d like help decoding a stamp (or the absence of one), send us a clear photo of the mark and the whole piece. We’ll happily translate those tiny hieroglyphs and tell you what they mean for date, origin and care.