Is Your Jewellery As Safe As You Think?

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What is it?
A ring in the shape of a numbat. It was bought in a local opportunity shop in Perth, so the origins of the ring are unknown.

Why was the ring tested?
The owner of the ring has an allergy to nickel. When wearing the ring she noticed itchiness, especially in hotter conditions as the moisture would heighten the symptoms.
To determine the cause, the ring was scanned with an XRF.

What was the method for testing?
The ring was tested on the handheld Bruker S1 TITAN 800 XRF. The ring was run for 60 seconds on the ROHS calibration mode. A silica and an OREAS 45d standard were used to ensure the calibration was working.

What was discovered?

As predicted, the ring contained a high density of nickel, which equated to roughly 51%.

However, the ring also contained roughly 1% of cadmium, which is concerning. Cadmium, if found at all, should be below 0.01%. This meant that the ring contained 100 times more cadmium than the recommended amount.

The ring also contained 34% copper and 19% zinc, which is normal to find in jewellery.

Looking deeper into the spectrum

During data processing it became apparent that there was a false antimony reading. This was concluded as a false reading as antimony presented itself in the numerical data but was not in the spectra.

To be a true reading of an element, there needs to be two peaks within the spectra; the alpha and the beta. This correlates to the atomic structure of the element and is therefore known where the peaks will lie. The alpha and beta can come from the K, L, or M rings of the atom.

Spectra 2: Focus on cadmium peaks.

Spectra 2 is a zoomed in graphic of the cadmium peaks. Cadmium is identified in the blue label and antimony in the pink. As seen in the spectra 2, cadmium has two peaks. Where the label lies for cadmium is the K alpha peak, which is 23.173. The K beta is the smaller peak which is located at 26.093. As both of these peaks are present, it is safe to assume this is a positive reading for cadmium.

Antimony in the spectra only has one peak, which is why this is a false reading. A likely cause of this is because the K alpha for antimony is 26.359 and the K beta for cadmium is 26.093. The instrument likely picked up the signal and corresponded it to the wrong element.

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