You can freely build on How Chemically Strengthened Glass Works

What this patent covers

This patent details a specific chemical composition for sodium aluminosilicate glass designed to be strengthened through ion exchange. By immersing the glass in a molten salt bath, smaller sodium ions in the glass surface are replaced by larger monovalent ions, such as potassium. Because these larger ions are forced into the space previously occupied by smaller ones, they create a crowded, compressed surface layer that acts like armor, making the glass significantly more resistant to breakage.

What is now free to use

All 0 claims of US 3778335 are in the public domain. Specifically:

The 0 dependent claims add narrowing limitations and are also free.

What is NOT covered

Patent expiry frees this specific invention. Separately-patented improvements made after expiry may still be protected.

• Does not cover glass strengthened by thermal tempering (rapid cooling).

• Does not cover glass compositions lacking the specific ratio of MgO and ZrO2 defined in the claims.

• Does not cover the physical process of ion exchange itself, only the specific glass chemistry that makes it effective.

Who is building on this today

Corning remains the primary innovator in this space, having evolved this 1970s chemistry into the modern Gorilla Glass product line. Other major glass manufacturers like AGC Inc. and Schott AG also utilize similar ion-exchange principles for their own high-strength display glass products.

Products built on expired version of this technology

How to cite this patent in your documentation

Corning Glass Works. US Patent 3778335. Sodium aluminosilicate glass article strengthened by a surface compressive stress layer. Granted 1973, expired 1991. Now in the public domain.

Note: This is a convenience citation. Consult a patent attorney for formal freedom-to-operate analysis.

PatentBrief is an educational resource and does not provide legal advice. Patent expiration information is derived from USPTO records and may not reflect continuation patents, divisional filings, or separately-patented improvements. For commercial use or production decisions, obtain a formal freedom-to-operate (FTO) opinion from a registered patent attorney.