Apple Watch: What is ion-strengthened glass and how is it made?

Sapphire has been the talk of the Apple community ever since the company partnered with GT Advanced in a failed effort to mass produce the material. While much is known about sapphire production, very little has been discussed about Apple’s ion-strengthened glass, which graces the front of the iPhone 6, the iPhone 6 Plus and now the Apple Watch Sport.

Unlike sapphire, which is artificially made in a process that requires extreme heat and pressure, ion-strengthened glass is glass that has been chemically altered via ion exchange to improve its strength. In this process, the sodium ions in the glass material are exchanged with larger potassium ions under high temperature. This is a cost-efficient process that produces a material more impact resistant and scratchproof than regular glass.

The process involves heating glass, which routinely is treated with sodium to lower its melting temperature, and soaking it in a bath of potassium salt. This allows the smaller sodium atoms to diffuse out of the glass and the larger potassium atoms to move into the material. The larger atoms compress the glass and strengthens it so it is less resistant to impact and scratches. For a hands-on explanation, check out this video from Applied Science that both explains and then demonstrates this ion-exchange process.

Ion-exchange is a common process to strengthen glass and is used by a variety of companies to produce display material for mobile and wearable devices. Though the methods are similar, each company tweaks the process to improve the final product to suit its needs. Corning uses ion exchange in the production of its Gorilla Glass material for smartphones and tablets, while Apple uses it for the Watch’s Ion-X glass and the iPhone’s ion-strengthened glass.