# How Chemically Strengthened Glass Works > A 1971 Corning patent describing a specific chemical recipe for glass that can be made incredibly tough by swapping small atoms in its surface for larger ones. - **Patent:** US 3778335 - **Original title:** Sodium aluminosilicate glass article strengthened by a surface compressive stress layer - **Owner:** Corning Glass Works - **Granted:** 1973 - **Status:** Public domain (expired) - **Times cited:** 52 - **Field:** consumer_electronics, materials, mechanical ## What it does 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 it does NOT cover - 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. ## The clever bit The innovation lies in the precise balance of MgO and ZrO2, which allows the glass to undergo ion exchange efficiently while maintaining chemical durability and preventing the glass from becoming brittle. ## Real-world examples 1. Corning Gorilla Glass 2. Smartphone display covers 3. High-durability tablet screens ## Why it matters This technology is the direct ancestor of the ultra-durable cover glass found on almost every modern smartphone. By enabling thin, lightweight glass that resists shattering, it allowed for the design of the flat, touch-sensitive screens that define the mobile computing era. ## Frequently asked questions ### What does How Chemically Strengthened Glass Works cover? A 1971 Corning patent describing a specific chemical recipe for glass that can be made incredibly tough by swapping small atoms in its surface for larger ones. ### Who owns patent US 3778335? Corning Glass Works owns this patent, granted in 1973. ### When does this patent expire? This patent has expired and is now in the public domain — anyone can use the invention freely. ### What is patent US 3778335 cited by? This patent has been cited by 52 later patents that build on its ideas. ### What problem does this patent solve? This technology is the direct ancestor of the ultra-durable cover glass found on almost every modern smartphone. By enabling thin, lightweight glass that resists shattering, it allowed for the design of the flat, touch-sensitive screens that define the mobile computing era. ### What does this patent NOT cover? Does not cover glass strengthened by thermal tempering (rapid cooling). **Full plain-English explainer:** https://patentbrief.org/patent/us/3778335/gorilla-glass-chemically-strengthened **Original patent:** https://patents.google.com/patent/US3778335 --- _Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._ ## Related patents Semantically similar inventions in the PatentBrief corpus: - [How Lithium-Cobalt Battery Cathodes Were Invented](https://patentbrief.org/patent/us/4302518/lithium-ion-battery-cathode) — This 1981 patent details the chemistry behind the lithium-cobalt oxide cathodes that power almost every modern smartphone, laptop, and electric vehicle. - [How Plastic Soda Bottles Are Made Stronger Using Stretched Molecules](https://patentbrief.org/patent/us/3733309/pet-plastic-bottle) — A 1970s invention that describes how to make lightweight, clear plastic bottles strong enough to hold carbonated drinks without exploding. - [How Lithium-Ion Battery Cathodes Are Made](https://patentbrief.org/patent/us/4357215/lithium-ion-cathode-goodenough) — A foundational 1982 method for creating the materials used in rechargeable lithium-ion batteries by removing ions at low temperatures. - [How the Float Glass Process Makes Perfectly Flat Window Panes](https://patentbrief.org/patent/us/2911759/float-glass-pilkington) — This 1954 patent describes the float glass process, a method for creating high-quality, perfectly flat glass by floating molten glass on a bath of liquid metal. - [How Corning Invented Modern Fiber Optic Cables](https://patentbrief.org/patent/us/3711262/optical-fiber-waveguide) — A 1970 method for creating glass fibers that carry light over long distances by layering glass inside a tube and drawing it into a thin, solid strand.