Ceramic Shield

It’s the toughest glass on any smartphone. So what is it and how does it work?

-  CARRIE MARSHALL

THE iPHONE 12 range includes a new kind of glass: Ceramic Shield. It’s four times tougher than the glass in the iPhone 11 handsets, and it’s both harder and more scratch–resistant too.

Like most of the smartphone glass in the world, Ceramic Shield was developed in association with Corning of Gorilla Glass fame. What makes this glass different is that it contains tiny ceramic nano–crystals embedded in the structure. Those crystals have a more regular structure than glass, and if you embed them in the right way they can make the glass stronger and more impact–resistant.

You’ve seen ceramics in Apple products before: it’s made several ceramic versions of the Apple Watch. You might also recall that none of those ceramic cases were transparent. That’s because ceramics’ stronger structure means they are usually opaque, which isn’t ideal for device displays; when they’ve been used in phones before by firms such as Samsung they’ve been used to create decorative glass backs, not transparent front screens.

But there’s a middle ground between ceramic and glass called glass–ceramics. Glass–ceramics offer the best of both worlds for screens, combining the transparency of glass with the toughness of ceramics.

According to Corning, glass–ceramics “start life as a glass and then transform into a nearly completely crystalline, or ceramic, substance. This happens under an intense application of carefully controlled heat and the addition of a nucleating agent — silver or titanium, for example — that forms ‘seeds’ around which crystals can grow.” Apple describes this process as a “high temperature crystallization step” and it creates crystals that are so small they don’t impede the transparency.