Some Fact Checking Please

For once, the title, "This Porcelain Is Tougher Than It Looks," is correct, but the article gets the basics wrong:

Wallace Chan, the Hong Kong jeweler behind some of the world’s most exclusive gems, sat in a sunny Manhattan hotel room a few weeks ago, talking about his latest creations.

He displayed one, a large blue ring topped with a diamond — and began whacking it aggressively against the wooden coffee table.

Bang! Mr. Chan, 62, just smiled. Then he rapped it again.

The ring was primarily made of porcelain, a ceramic normally used for rose-strewn tea sets and figurines of pouting milkmaids, and such treatment should have reduced it to a handful of shards on the hotel room carpet.

But this wasn’t just any old porcelain. It was a porcelain seven years in the making, which Mr. Chan invented and which he says is five times harder than steel.

The material — called for the time being, a little unimaginatively, Wallace Chan Porcelain — is made of specially chosen ingredients that Mr. Chan treats like the equivalent of a state secret out of fear of industrial espionage (the jewelry world is, apparently, a paranoid place). But the ingredients are, he said, almost devoid of impurities.

All high fire (vitrified) clays, like porcelain, and most of the low fire clays, are MUCH harder than steel.

Ordinary glass is harder than steel, which you can demonstrate if you (very) carefully try to drill window glass.

On the Mohs Scale, steel is typically in the 4-4½ range, and porcelain is around 7. (Talc is 1 & diamond 10 on the Mohs Scale)

What Mr. Chan has done is create a TOUGHER ceramic, which is important, but VERY different from a HARDER ceramic.

He does this, as the article reveals, by making small (but important) changes in the formulation of porcelain, and firing it at a higher temperature, which further reduces voids in the resulting fired ceramic.

It's pretty much the same process used by people trying to put ceramics in things like jet turbines, though he seems to have come up with a technique that does not require the elaborate tooling used for those applications.

My guess his recipe is that, "Almost devoid of impurities," is the most important bit.  

Ceramics yield very little, which means that stresses at any crack tips are very high because there is little local yielding, so the elimination of inclusions are critical to toughness and tensile strength.

Good for Mr. Chan, but someone needs to give the reporter a class in material science 101.