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Gorilla Glass vs. sapphire on new Apple devices?

Corning CEO: We keep our secrets

Ahead of Apple's new product announcement Tuesday, the chairman and CEO of Corning made his case for why mobile device makers should use his company's Gorilla Glass over competing sapphire crystals.

The current iPhone screens are made with Gorilla Glass. "We originally invented Gorilla [Glass] for Steve Jobs and Apple," Corning's Wendell Weeks said in a "Squawk Box" interview on CNBC.

Rumors have run rampant on the Internet about whether the expected new iPhone will ditch the Gorilla Glass screens in favor of sapphire or whether the rumored Apple smartwatch would have a sapphire face.

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While refusing to address any of these reports, Weeks jokingly said: "Regretfully, I'm going to keep Apple's secrets."

But he did talk extensively about the pros and cons of the two materials. "We've made a lot of sapphire in the past," he said. "[But] we're invested strongly in Gorilla as opposed to sapphire overall."

"Sapphire is good in that it's scratch resistant. That's its main feature. It's why you have it on your watches because you don't drop watches," Weeks said, claiming that sapphire tends to be more brittle. "Gorilla Glass drop performance is much better." He also said Gorilla Glass is less expensive and lighter.

He did concede that both are "legitimate choices," and it's going to come down to "who can innovate the materials best."

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The sapphire versus Gorilla Glass speculation started last year, when sapphire maker GT Advanced Technologies entered into a multiyear supply agreement with Apple.

In a company overview released last month, GTAT said, "[Its] newly expanded sapphire materials business with Apple is expected to add recurring revenue base to business."

GT Advanced Technologies said it had no comment.

—By CNBC's Matthew J. Belvedere