Visiting the Birmingham Assay Office Gemmology Lab: Pearl Testing, X-Ray Scans, and Grading Explained
- Dimitri
- Apr 14
- 5 min read
Last week, I had the chance to visit one of the coolest places in the UK gem world – the Birmingham Assay Office Gemmology Lab. This was actually my third time visiting, and every time I go, I learn something new.
First, a little history. The Birmingham Assay Office has been around since 1773, mostly known for hallmarking precious metals. But their gemmology lab is much newer, starting in 2000. They set it up to help with gem testing, diamond grading, and specialist reports for the jewellery trade. The lab works very closely with SafeGuard, their valuation department, to make sure everything tested is properly identified, assessed, and valued. Over the years, they’ve built a strong reputation for being accurate, trusted, and very high tech.
Walking around the lab, you really get to see how advanced they are. They use specialist equipment like DiamondSure™ and SYNTHDetect for spotting synthetic diamonds, the DiamondView™ to reveal diamond growth patterns, Raman and FTIR Spectrometers to identify gemstones and detect treatments, and the Sarine DiaMension™ system for measuring diamond proportions. For pearls, they have dedicated X-ray machines that help figure out if a pearl is natural, cultured, beaded, or non-beaded. It’s seriously impressive to see all these tools in action.
When it comes to gem testing in the UK, they’re definitely one of the best places to go.
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My journey started early. I left Cardiff on a direct train to Birmingham New Street – just two hours, really easy. From there, I jumped in a taxi straight to the Assay Office, tucked away on Moreton Street in the Jewellery Quarters. The building is sleek and modern, and when you walk in, you know straight away you’re somewhere special.
I didn’t just visit for fun though – I brought a strand of pearls and some gems with me to get tested!
The team of highly trained Gemmologists welcomed me in and took me through the whole pearl testing process. It was fascinating.
First up, X-rays. They have this super old-school Hewlett Packard 43805N X-ray system (definitely older than me 😂). Even though it’s an older model, it’s still amazing for showing the internal structure of pearls.
Watching them work was like stepping back in time, but in the best way. They placed my pearl strand carefully onto a special plate and zapped it with X-rays. Then came the really fun part – developing the film by hand. It felt like a mix between a science lab and an old photography studio!
Once the film was ready, we sat down and looked at each pearl using a loupe. This part was a real eye-opener. We were checking if the pearls were beaded or non-beaded.
Beaded pearls have a little round bead inside, which shows up clearly on an X-ray – it looks like a neat circle in the middle. Non-beaded pearls, on the other hand, are made up completely of nacre (that beautiful shiny pearl material) and have no bead inside. They look more solid and natural all the way through.
Spotting the difference is a big part of figuring out how the pearl was grown and how valuable it might be. It takes a sharp eye and a lot of practice!
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After that, it was time for another X-ray, but this time using a more modern machine. This one checks the chemical makeup of the pearls to figure out if they are freshwater or saltwater.
It’s really clever how they do it. Different types of pearls have slightly different chemical elements inside them. Freshwater pearls (grown in rivers and lakes) usually have higher levels of manganese and less strontium. Saltwater pearls, like South Sea, Akoya and Tahitian, show the opposite – higher strontium and lower manganese. South Sea pearls, in particular, have really strong strontium signals because of where they grow.
By measuring these tiny traces, the lab can tell if a pearl is freshwater or saltwater and even get clues about where in the world it was grown. It’s amazing how much information you can get just from the tiniest pieces of the pearl’s structure!
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Once all the testing is done, the pearl strand moves on to grading. They use the GIA’s 7 Pearl Value Factors – size, shape, colour, lustre, surface quality, nacre quality, and matching – to give a full, detailed report.
Each factor tells you something different about the pearls:
Size: Bigger pearls are usually rarer and more valuable. They measure each pearl carefully to see how large it is.
Shape: Perfectly round pearls are the most classic (and the hardest to find!), but other shapes like oval, drop, and baroque are loved too.
Colour: Pearls come in many colours, from classic white to pink, gold, silver, and even peacock green. The lab looks at the bodycolour and any overtone (that extra shimmer you sometimes see).
Lustre: This is all about how shiny the pearl is. A really high-quality pearl will have a sharp, bright reflection – almost like looking into a mirror.
Surface quality: They check how clean the surface is. Pearls are natural, so tiny marks are normal, but fewer blemishes usually mean a higher grade.
Nacre quality: This looks at how thick and smooth the nacre is (that’s the layers of pearl material). Good nacre gives the pearl its strength and rich glow.
Matching: For strands like mine, they look at how well the pearls go together – not just in size, but in colour, shape, and lustre too. The better they match, the more beautiful the strand looks overall.
Grading pearls is a really careful process, and it’s amazing to see how much work and time goes into it behind the scenes. Every tiny detail makes a difference!
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I left the Birmingham Assay Office feeling completely blown away. Watching the pearls go through testing, X-rays, chemical analysis, and grading was like seeing science and art come together. Every little step – from checking if a pearl is beaded or non-beaded, to finding out if it’s freshwater or saltwater, to grading it with the GIA 7 Value Factors – showed just how much skill, time and detail goes into pearl testing.
It was such a fun and inspiring experience, and a huge thank you to the amazing gemmologists who took the time to walk me through the whole process.
To finish the day, we snapped a photo together – a memory I’ll always treasure from my third visit to this incredible laboratory.
If you ever get the chance to visit the Birmingham Assay Office Gemmology Lab, I can’t recommend it enough!
To learn more about The GIA 7 Pearl Value Factors visit the GIA's website HERE
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