Indeed, "artificial diamond" is one of the top examples of the first definition of "artificial" at Merriam-Webster, which is "man-made." [1]

Etymologically it means "made by skill."

But I understand the hesitation to use the word, as it gives an impression of "fake."

https://www.merriam-webster.com/dictionary/artificial

A man-made television isn't an artificial television; a man-made taco isn't an artificial taco.

Man-made beef and artificial beef are both the same thing: a not-beef beef substitute. Beef is by definition cow-made.

Man-made diamonds are just diamonds.

Last I heard from the forefront of geology and ecology, "natural" televisions and tacos have yet to be found.

So I don't think the distinction is best analyzed with examples like that.

If something is normally created and nature, and humans find a way to reproduce it, it is common to call the human produced versions artificial even if the result is identical in principle.

Humans make lots of distinctions that fall apart if we get too pedantic, but have useful casual, cultural, or practical associations and meanings.

Burn hydrogen to make water. Is that artificial water? Or is it forever artificial water? Is all water that mixes with it artificial water? Is all water now artificial since it has mixed with human made water?

While the basic definition seems to be merely "man-made", I would say it holds there is some underlying distinction between the natural and artificial. Natural light vs artificial light -- the two are distinctly different. But are the photons produced by a light bulb artificial, or are they natural photons?

Artificial diamonds are more diamond than diamonds. The diamond portions are identical, regardless of origin.

Or maybe there are trapped gasses or other identifiers left in them that make them distinct. I don't really know about this point.

Anyhow, the natural vs artificial distinction really seems to break down when things are (literally) physically and chemically identical.

That's not what makes things artificial vs natural. Artificial vanillin is "more vanilla than real vanilla". A natural vanillin molecule is indistinguishable from fully synthetic vanillin from crude oil. The latter is still called "artificial flavor".

Artifical vanillin is not the whole package though, as there are other compounds in natural vanilla that make up the flavour, so it doesn't reflect the full product. "Natural" vanilla extract may also never have seen a vanilla bean, as it could be plant derived, or even from a beaver's ass.

Until the rise of synthetics the perfect diamond had no flaws or impurities. Now the language has changed and apparently it's all about just the right number of imperfections and impurities, though those will also be mimicked in short order (if they haven't been already).

There is a genuine physical reason to prefer 'real' vanilla extract over artificial. Not so much for diamonds.

>Burn hydrogen to make water. Is that artificial water? Or is it forever artificial water?

This depends on whether you ask a scientist or a homeopathic practitioner.

> "natural" televisions and tacos have yet to be found.

I refuse to give up hope!