Why 18ct Gold Isn't One Colour

Have you ever laid two 18ct gold rings side by side and caught yourself doubting your eyes? One glows warm honey, another flares rosily, a third looks almost pale. The difference isn't a trick of the light. It is chemistry, and it is the most under-examined pleasure in fine jewellery.

The 25% That Changes Everything

Pure gold is a soft, saturated yellow, but at 18ct it is only seventy-five per cent gold. The remaining quarter consists of alloying metals, and that quarter dictates everything about the way the metal behaves, wears and reflects light. Copper pulls the tone towards blush; silver steadies it into a paler yellow; palladium or nickel creates the coolness we call white gold. Move the proportions slightly and you move from rose to red to something almost peach. For such a small fraction, the possibilities are surprisingly broad.

Green gold is perhaps the most misunderstood of these alloys. It is not a surface effect or a sign of low quality, but a deliberate blend in which silver—sometimes with a touch of zinc—cancels the familiar copper warmth. The result is a soft, lemony tint that can look extraordinary against deeper skin tones and in sculptural pieces. Because it is uncommon, it tends to catch the eye without shouting. Knowing that this shade is a property of the alloy, not a flaw, is useful when inspecting second-hand or vintage jewellery.

Reading the Hallmark, and the Metal

On British hallmarks, 18ct gold is marked 750, meaning seventy-five parts gold per thousand. But the hallmark won't tell you which metals fill the remaining 250 parts. That is why two '750' chains can look entirely different next to the same skin. You must train your eye to read the colour, and your fingers to know the weight and temperature of different alloys. A good jeweller will tell you exactly what is in the alloy, and which shade will flatter your skin tone or sit best beside other pieces you own.

This is also why repairs and resizing require care. The solder used to join two ends of an 18ct band is itself an alloy, and its melting point must be lower than the metal around it. When a careless repair is made, you may see a faint difference in colour at the seam. The best workshops, including our own, choose solder that matches the parent alloy closely and finish the piece so that no seam announces itself. The colour of 18ct gold is not a static fact; it is a language, and once you start noticing it, every jewel becomes more interesting.