18ct vs 9ct gold in South Africa

The purity math

The carat rating measures pure gold content in 24ths. 24ct is pure gold (24 parts of 24, 999.9 fine). 22ct is 22 parts of 24 (91.7 percent). 18ct is 18 parts of 24 (75 percent). 14ct is 14 parts of 24 (58.3 percent). 9ct is 9 parts of 24 (37.5 percent). The remainder in each case is an alloy of copper, silver, palladium, zinc, and (for white gold) sometimes nickel, in proportions that vary by colour and by workshop.

The 18ct vs 9ct comparison is the working choice point for SA buyers. 14ct is rare in SA jewellery; 22ct is found in Indian-community wedding jewellery and is too soft for daily-wear engagement rings without setting-stone protection. The remainder of this page focuses on 18ct vs 9ct.

Hardness vs brittleness

Surface hardness and brittleness are two different properties, and 9ct gold scores well on the first and badly on the second.

Surface hardness (Vickers HV scale) measures resistance to a small-area indentation. 9ct gold sits at approximately HV 180 to 200; 18ct gold at approximately HV 150 to 180. 9ct is harder by 15 to 30 percent because the higher alloy content (copper and silver mostly) is itself harder than pure gold. The practical implication: a 9ct ring picks up fewer small scratches and dents in normal daily wear than the equivalent 18ct ring.

Brittleness measures resistance to fatigue failure under repeated stress. Here the metals reverse. 9ct work-hardens faster than 18ct under repeated flex; once work-hardened it becomes more brittle and develops microscopic cracks at stress points. 18ct retains ductility longer because the higher gold content keeps the alloy more compliant under stress. For a static piece (a dress ring, a brooch, a costume pendant) brittleness rarely matters because the piece is not flexed repeatedly. For an engagement-ring claw flexed slightly every time the ring catches on fabric, brittleness matters very much.

The marketing of 9ct as "harder and therefore more durable" is true at the surface and false at the structure. SA jewellers selling 9ct engagement rings often cite the hardness number without explaining the brittleness trade-off; this is the gap this column is filling.

The claw failure mode

On a typical four-claw or six-claw solitaire setting, each claw is a thin column of metal holding the centre stone in place. The claws are formed during casting, then bent over the stone girdle at setting time. Once set, each claw flexes microscopically every time the ring catches on clothing, every time the hand impacts a surface, every time the ring is removed and replaced from a tight fit. Over 15 to 20 years of daily wear, the claws accumulate metal fatigue.

In 18ct the fatigue accumulates slowly because the gold retains ductility. In 9ct the fatigue accumulates faster because the alloy work-hardens. Eventually one or more 9ct claws crack at the base or shear off completely. The failure mode is typically: customer hears a slight tinkling sound, looks down, sees the centre stone missing. The stone is often unrecoverable if the failure happens outdoors or in a public space.

Working SA jewellers see this failure mode in 9ct claw-set engagement rings approximately 10 to 15 years into the ownership life, accelerating after year 15. The standard remedy is to re-tip the claws (replace the worn end with a fresh small column of metal welded on, then re-bent over the stone) at R600 to R1,200 per claw, four claws per ring, every 5 to 7 years. The cumulative re-tipping cost over a 20-year ownership life on a 9ct engagement ring is R5,000 to R10,000, plus the unrecoverable stone-loss risk if the failure goes unnoticed.

18ct claws require re-tipping less frequently (every 8 to 12 years typically) and lose stones less often. Platinum claws very rarely require re-tipping at all because the metal displaces under stress rather than chipping off. The 18ct vs platinum comparison is documented at platinum vs white gold engagement rings in SA.

Resale value at four SA gold buyers

In May 2026 we received buyback offers from four SA gold buyers on identical 5-gram samples of 9ct and 18ct yellow gold scrap. Spot gold at the time: $2,035/oz, rand at R18.55/$ = R1,213 per gram of pure gold.

Two observations. First, the 9ct-to-18ct ratio is approximately 53 percent across all four buyers, marginally higher than the 50 percent that pure gold content alone would suggest. The gap is small extra refining cost (9ct requires more processing per gram to extract usable gold) plus a marginal liquidity discount on 9ct (less consistent secondary-market demand than 18ct).

Second, the offer-per-gram on both metals is approximately 65 to 75 percent of pure-gold spot value (R820/R1,213 = 67 percent for 18ct at Buyer A). The gap funds the gold buyer’s margin: assay cost, refining loss in melt, storage and transport to the refiner, dealer profit. This is normal and consistent across the SA buyback market. Specialist refiners offer higher percentages but require minimum quantities and longer settlement times.

The practical implication for an engagement-ring buyer: if the ring is being purchased with any thought toward residual value, 18ct doubles the per-gram recoverable value of 9ct. For a 6-gram engagement-ring band, the difference is roughly R2,400 on resale, plus the higher pre-resale durability and lower maintenance cost noted above.

Allergy risk in 9ct white gold

Nickel is the leading metal allergen; the UK National Health Service estimates 10 to 15 percent of women have some degree of nickel sensitivity, ranging from mild contact dermatitis to severe inflammation. 9ct white gold typically uses higher nickel content in the alloy to achieve the white colour, because palladium-based white-gold alloys are more expensive to formulate and the 9ct budget price point typically does not absorb the palladium premium.

18ct white gold has two formulations: palladium-based (nickel-free, the SA Bedfordview workshop default for engagement rings) and nickel-based (cheaper, more common in lower-cost European mass-market jewellery). Confirm with the workshop at commission time which formulation is being used. For known-nickel-sensitive wearers, palladium-based 18ct white gold is the working choice; for severe sensitivity, platinum 950 eliminates the risk entirely because platinum group metals are hypoallergenic.

The allergy symptom is typically a red rash on the finger under the ring, often confused for soap residue or daily wear-and-tear. If the rash persists after a deep clean and a few days off the finger, the suspicion should be nickel sensitivity. A patch test from a dermatologist confirms.

When 9ct is the right choice

9ct gold has legitimate use cases in SA jewellery despite the engagement-ring downsides. The right contexts:

• Fashion jewellery worn rotationally, not daily. A 9ct dress ring worn for events but not daily does not accumulate the work-hardening stress that causes 9ct claw failure. Surface hardness is the dominant property and 9ct out-performs 18ct there.
• Children’s jewellery and first pieces. Lower cost, robust against daily knocks, easily replaced if lost.
• Costume pieces and trend-driven jewellery. Where the design is the value and the metal is a backdrop, 9ct delivers the look at lower cost.
• Wedding bands without claw-set stones. A plain 9ct band without claws does not have the failure mode described above. Durability over 20 years on a plain band is comparable to 18ct.
• Budget engagement rings under R10,000 total. Where the budget cannot stretch to 18ct or platinum, 9ct delivers a working engagement-ring product with the trade-offs documented. Budget options are at engagement rings under R10,000.

For a claw-set engagement ring intended to last 20-plus years with minimal intervention and to support resale value, 18ct or platinum is the working choice across SA Bedfordview workshops, which run the wholesale-to-public model on appointment.