I am interested in learning how to oxidize tantalum. I have seen some tantalum rings that the sellers say is a permanent smokey blackish color. But I've spoken to some people that say tantalum cannot be oxidized, and the rings I saw must have been coated.

So anyone know if and how tantalum can be oxidized?

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    $\begingroup$ It is probably anodized, like niobium (sometimes used for colorful earrings) and titanium. Tantalum is now relatively expensive, because of the "coltan" conflict minerals issues and so on. But tantalum has industrial uses, e.g., for Ta capacitors and acid-resistant vessels, and it is less expensive (last time I checked my favorite element sourcing web site) than platinum, gold or palladium. Check out wiki for more information. $\endgroup$ – Ed V Jun 21 '19 at 0:01
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    $\begingroup$ Any metal can be oxidized. Although Ta is rather resistant, there's lots of ways. As for the black color, it might be tantalum nitride, but this question falls under both unclear and too broad, IMO. $\endgroup$ – Mithoron Jun 21 '19 at 23:18

The smoky black stuff is probably not tantalum oxide. The only such oxide that's well characterized is $\ce{Ta2O5}$, which is white. Tantalum itself is a rare element, so if the jewelry contains tantalum at all it's probably a thin coating or cladding on a base metal substrate.

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