How many of us are toting around smartphones with cracked and scratched screens? No need to raise your hand; we can’t actually see you. Now imagine that your phone screen was continuous exposed to the elements in a position on your body where it can easily get scratched, and you’ve imagined the life of an Apple Watch. So can the pricey accessory take a licking and keep on… well, not ticking exactly, but you get the idea.

Our colleagues at Consumer Reports purchased some Apple Watches (both the aluminum Apple Watch Sport and the more expensive stainless steel version; but not the $10,000 gold watch) last week and took them right into the labs to put the new devices through its paces.

The Sport uses hardened “Ion-X” glass for its watch face. Ion-X appears to be similar to Corning Gorilla Glass, which you’ll find on a lot of smartphones.

The stainless steel Apple Watch actually uses a super-hard sapphire-crystal face favored by high-end companies like Rolex (not to be confused with Ronex, a brand you can buy from a street vendor for less than the cost of a Whopper).

To test scratch resistance on the watches, CR turned to the old Mohs hardness scale that you hopefully remember from middle school science. You remember, gypsum can scratch talc, quartz can scratch gypsum, topaz can scratch quartz, and diamonds are forever, at least according to Shirley Bassey.

Just like the Batcave, the CR labs happen to have a Mohs hardness kit that applies pressure using picks of varying hardness to determine where a material falls on the scale.

“The Mohs scale uses common materials, so it’s easy to understand,” explains James A. Harrington, a professor of materials science and engineering at Rutgers University. “When it comes to their structure, glasses and crystals are as different as apples and oranges.”

While glass is a generic term that can mean a lot of things, sapphire is a mineral with a Mohs rating of 9/10, just below diamonds. And as you’d expect, the sapphire crystal watch face went unscratched even up to a 9 on the Mohs kit.

The Ion-X glass face was almost as impressive, only scratching when tested with a level-8 pick on the Mohs kit.

For a non-scientific test of the Sport, CR also tried to scratch the glass with a steel key but to no avail.

In response to people who have pointed out that some sandpaper can scratch the Apple Watch face, CR points out that corundum, with its Mohs score of 9, is commonly used in sandpaper.

“So it’s not that suprising that sandpaper would scratch the glass of the Apple Watch Sport,” writes CR’s Glenn Derene. “The lesson: Keep your belt sander away from your Apple Watch Sport, and keep your diamond rings away from your Apple Watch.”

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