White Gold, Rose Gold, and Yellow Gold: Alloy Composition, Colour Science, and Hallmarking

Gold in its pure form (24K/999) has a characteristic warm yellow colour. But the gold jewellery market offers a spectrum of colours — yellow, white, rose, and occasionally green — achieved through alloying with different metals. Understanding these alloys is important for both jewellers and consumers, particularly when it comes to hallmarking and purity certification.

The Science of Gold Colour

Pure gold is yellow because of the way its electrons interact with light. The relativistic effects on gold's outer electrons cause it to absorb blue wavelengths of light and reflect yellow, orange, and red wavelengths. When other metals are alloyed with gold, they change the electronic structure and shift the colour.

Yellow Gold

Yellow gold is the traditional standard in Indian jewellery, particularly at 22K (916 fineness). The typical alloy composition for 22K yellow gold is 91.6% gold, approximately 5% silver, and approximately 3.4% copper.

The silver and copper together maintain the warm yellow colour while adding the hardness needed for wearability. Slight variations in the silver-to-copper ratio produce subtle shade differences — more silver creates a lighter, greener yellow; more copper creates a warmer, redder yellow.

For 18K yellow gold (750 fineness), the alloy typically contains 75% gold, 12.5% silver, and 12.5% copper. The higher proportion of alloying metals creates a slightly paler yellow compared to 22K.

White Gold

White gold achieves its colour by alloying gold with white metals that counteract gold's natural yellow:

Palladium-based white gold (the preferred formulation) contains 75% gold and approximately 25% palladium. Palladium effectively bleaches the gold colour and produces a natural white appearance. This alloy is more expensive due to palladium's price but is hypoallergenic.

Nickel-based white gold contains 75% gold, approximately 15% nickel, and smaller proportions of copper and zinc. Nickel is effective at whitening gold and is less expensive than palladium, but can cause allergic reactions in some people. EU regulations restrict nickel in jewellery for this reason.

Most white gold jewellery is additionally rhodium-plated — coated with a thin layer of rhodium (a platinum-group metal) to enhance its bright white appearance. This plating wears over time and needs periodic reapplication.

White gold is predominantly made at 18K (750) or 14K (585) fineness. 22K white gold is extremely rare because there is insufficient room for whitening metals at 91.6% gold content.

Rose Gold

Rose gold (also called pink gold or red gold) gets its warm, pinkish hue from a higher proportion of copper in the alloy:

18K rose gold typically contains 75% gold, approximately 22.5% copper, and approximately 2.5% silver. The dominant copper content creates the distinctive pink colour.

14K rose gold contains 58.5% gold and more copper, producing a deeper, more saturated pink.

The more copper in the alloy, the deeper the rose colour. Higher-karat rose gold (closer to 22K) has a more subtle pink tint because the larger proportion of yellow gold dilutes the copper colour.

How Coloured Gold Is Hallmarked

From a hallmarking perspective, the colour of the gold is irrelevant — what matters is the fineness. An 18K white gold ring and an 18K rose gold ring both receive the same hallmark: BIS logo + 750 + HUID.

The XRF test at the hallmarking centre measures the total gold content as a percentage of the alloy. Whether the remaining 25% is palladium (white gold), copper (rose gold), or a silver-copper mix (yellow gold), the gold content determines the karat grade.

This means the hallmark tells you how much gold is in the piece but does not specify the colour or the alloying metals used. Consumers should rely on the jeweller's description for the colour type and the hallmark for the purity.

Surface Treatments and Testing Considerations

Rhodium plating on white gold presents a specific consideration for XRF testing. Since XRF measures surface composition, a rhodium-plated article will show rhodium in the analysis. Experienced hallmarking centres account for this by testing on an area where the plating has been removed or by recognising rhodium as a surface coating rather than a constituent of the gold alloy.

Two-tone and multi-colour jewellery — Articles combining yellow and white gold, or rose and yellow gold, are tested at multiple points to verify that each coloured section meets the declared purity.

Consumer Guidance

When purchasing coloured gold jewellery, verify the hallmark and HUID as you would for any gold article — the hallmarking process is identical regardless of colour. Ask the jeweller about the specific alloy composition if you have skin sensitivity concerns (particularly relevant for nickel-based white gold). Understand that the colour does not indicate purity — 18K yellow, 18K white, and 18K rose are all 75% gold. For white gold, ask whether the piece is rhodium-plated and understand that the plating will need periodic refreshing.

The Growing Market for Coloured Gold

Consumer demand for rose gold and white gold has increased significantly in India, particularly among younger buyers and for contemporary design jewellery. This trend has expanded the range of alloy compositions that hallmarking centres test, but the fundamental process remains the same: measuring the proportion of pure gold and certifying it against IS 1417 standards.