White Gold, Explained
This post has been extracted from an article by Dippal Manchanda, Technical Director & Chief Assayer at Birmingham Assay Office. Read the full article here.
White gold has long been a popular choice in the jewellery industry, valued for its elegance and versatility. But, what is white gold? What is it made of and how does it get its signature finish? In the UK, regulations about how precious metal jewellery is tested and described are put in place to protect consumers. This article has helpful information and background to ensure both industry professionals and consumers can make informed decisions when purchasing white gold jewellery
Gold, in its purest form, is naturally yellow. To achieve different colours, gold is often alloyed with other metals to give it a white or pink tone. An ‘alloy’ is a mixture of two or more metals, often created to influence a metal’s colour or durability. To create ‘white gold’ and achieve a white hue, gold is alloyed with another metal like palladium or silver. It is then usually plated with Rhodium to give it a finished white hue.
For decades, the term ‘white gold’ was loosely applied to any gold alloy that appeared white, even if it had a yellow or greyish hue. With so much variation, there was a need to standardise what constitutes ‘white gold’. This work was undertaken by Birmingham Assay Office in collaboration with Cookson Precious Metals. This work culminated in the adoption of an industry-wide definition, known as the MJSA Definition, which is now accepted around the world.
Not all alloys produce the same degree of whiteness. The ASTM Yellowness Index categorises 3 different standards of white gold alloys, creating a robust determination of what can and cannot be described and sold as white gold. These categories give clarity to consumers, manufacturers and retailers alike. According to this Index, a gold alloy can only be described as ‘white gold’ if it falls below a Yellowness Index score of 32.0.
The 3 categories of the Yellowness Index are:
- Premium Grade White Gold (Yellowness Index of less than 19.0). This is naturally white, and does not require any Rhodium plating.
- Standard Grade White Gold (Yellowness Index between 19.0 and 24.5). This is a mostly white alloy, and Rhodium plating is optional.
- Off-White Grade White Gold (Yellowness Index between 24.5 and 30). This alloy has a noticeably yellowish tint and needs Rhodium plating to give the alloy a white finished appearance.
We can also understand white gold alloys based on their composition and how each component added to an alloy can influence the final colour result.
- Silver whitens the alloy but can introduce a greenish hue
- Palladium whitens the alloy but adds a slight reddish tint
- Nickel is a strong whitener for an alloy
- Zinc also acts as a whitener
- Copper reduces yellowness in an alloy but also increases redness
No matter what the alloy for white gold contains, the final composition must contain set standards of pure gold to meet fineness or carat requirements.
This includes:
- 375 or 9ct alloys: these must contain 37.5% gold
- 585 or 14ct alloys: these must contain 58.5% gold
- 750 or 18ct alloys: these must contain 75.0% gold
In the past, it was extremely difficult to create a white gold alloy that met the requirements for 916 or 22ct gold. This fineness must contain at least 91.6% pure gold, which gives it a strong yellow colour and a limited scope for alloying. However, recent advancements in metallurgy have made it possible to produce a 22ct white gold alloy. Combined with Palladium, this creates an off-white alloy, opening up new possibilities for high-purity white gold jewellery!
All these guidelines on fineness and description provide an objective basis for defining white gold beyond its surface appearance, ensuring consistency in grading across different manufacturers and markets.
So, where does Rhodium Plating fit into this process? Rhodium plating is commonly applied to white gold jewellery to enhance its white finish. While rhodium is a bright, highly reflective metal, it is only a surface treatment and not part of the alloy. Over time, this plating wears off, revealing the true colour of the underlying gold alloy.
For jewellery that gets frequent wear, like rings or bracelets, rhodium plating may not be a long-term durable solution. The thickness and quality of rhodium plating affect its longevity, but ultimately, everyday wear will erode the plating and necessitate reapplication.
This poses a challenge for both the consumer and the retailer. To ensure transparency and maintain consumer trust, retailers should be clear about the composition of their white gold jewellery. Some key points to communicate include:
- Whether the jewellery is rhodium plated and why
- The natural colour grade of the white gold used
- The potential need for periodic rhodium re-plating
The distinction between true white gold and rhodium plated off-white gold is essential for:
- Consumers who deserve to know what they’re buying
- Retailers who must maintain trust and credibility
- Manufacturers who should strive for transparency and quality control
- Laboratories which need to ensure accurate testing and classification of white gold alloys
White gold is more than just a name—it is a scientifically defined material with measurable whiteness and a defined compositional standard. The research conducted by the Birmingham Assay Office and Cookson Precious Metals, led by Dippal Manchanda and Steven Henderson, has provided an objective framework for assessing white gold alloys, ensuring that the term is not misused. By prioritising education, transparency, and adherence to these standards, we can uphold the integrity of white gold in the jewellery industry.
Retailers and consumers alike should be equipped with this knowledge to make informed decisions. True white gold exists beyond rhodium plating, and recognising this distinction is key to maintaining quality and consumer confidence in jewellery.
Thank you to Dippal and the Birmingham Assay Office for this excellent resource for consumers to navigate white gold.
