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.
Original patent title: “Sodium aluminosilicate glass article strengthened by a surface compressive stress layer”
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. Granted to Corning Glass Works in 1973 with 52 forward citations, and it is now in the public domain.
Coverage
What does this patent actually cover?
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.
The gap
What does this patent 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 claimsclaimsThe numbered statements at the end of a patent that legally define what the inventor owns.Read more →.
- Does not cover the physical process of ion exchange itself, only the specific glass chemistry that makes it effective.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
Key facts
What made this novel
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.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Corning Gorilla Glass
Smartphone display covers
High-durability tablet screens
Why it matters
The bigger picture
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.
Filed
September 2, 1971
Granted
December 11, 1973
Market context
Who's building on this
Companies in this space
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.
Market impact
This patent laid the foundation for the chemically strengthened glass industry, enabling the transition from fragile soda-lime glass to the durable materials required for portable electronics. It effectively created the market for damage-resistant cover glass, which is now a multi-billion dollar sector essential to the global smartphone and laptop supply chain.
Claim 1 — Plain English
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.
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.
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.
Patent timeline
Application submitted to the patent office
Application published, typically 18 months after filing
Patent officially issued
Patent enters public domain
This patent is in the public domain
See the Freedom to Build guide — what is free to use, what is not, and how to cite this patent.
PatentBrief Score
Impact Score
Early stage
Citation count
34/40
Highly cited
Claim breadth
0/20
Narrow claimsclaimsThe numbered statements at the end of a patent that legally define what the inventor owns.Read more →
Recency
0/20
Older than 20 years
Assignee scale
0/20
Independent or smaller assigneeassigneeThe entity that owns the patent — usually the inventor's employer or a company.Read more →
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$29K – $92K
Midpoint $58K · expired or expiring · industry ×1.6
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Claim text not yet imported for this patent
Concepts involved
Citations
Patent lineage
Cite this patent
Boyd, D. (1973). How Chemically Strengthened Glass Works (U.S. Patent No. 3,778,335). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/3778335/gorilla-glass-chemically-strengthened
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
Embed
Add this patent to your site
Drop this plain-English patent card into any blog post or article — free, no signup. It always links back to the full breakdown here.
<div data-patentlens-widget data-patent-number="US3778335"></div> <script src="https://patentbrief.org/embed.js" async></script>
Stay in the loop
Get a weekly digest of new patents.
One email per week. No spam. Unsubscribe anytime.
Keep exploring
Related patents you should know
US 4683195 · 1987
How to Make Billions of Copies of a DNA Segment
This patent describes the Polymerase Chain Reaction (PCR), a method to rapidly create many copies of a specific piece of DNA or RNA, enabling its detection and analysis.
Cetus Corp
US 8697359 · 2014
How to Edit Genes in Human Cells Using an Engineered CRISPR System
This patent describes an engineered CRISPR-Cas9 system for precisely cutting DNA in eukaryotic cells to change how genes work, opening the door for gene editing in complex organisms.
Massachusetts Institute of Technology
US 7657849 · 2010
How the iPhone's Slide-to-Unlock Gesture Works
Apple's 2010 patent describes unlocking a device by dragging a specific graphical image across the touchscreen along a predefined path, a gesture that became iconic with the original iPhone.
Apple Inc
US 4733665 · 1988
How Doctors Implant a Permanent Stent Using a Balloon
This patent describes the method for placing a permanent, expandable wire mesh tube inside a blood vessel or other body tube using a balloon-tipped catheter to widen it and keep it open.
Expandable Grafts Partnership
US 4965188 · 1990
How to Make Many Copies of a DNA Piece with Heat
This patent describes the Polymerase Chain Reaction (PCR) method, a technique to make millions of copies of a specific DNA segment using a heat-resistant enzyme and repeated temperature changes.
Cetus Corp
US 4235871 · 1980
How to Encapsulate Active Materials in Lipid Bubbles Efficiently
This patent describes a method for trapping biologically active substances inside tiny, multi-layered fat bubbles called liposomes, using a specific water-in-oil emulsion and gel-forming process to improve how much material gets captured.
Individual
Semantically similar
You might also find these interesting
US 4302518 · 1981
How Lithium-Cobalt Battery Cathodes Were Invented
US 3733309 · 1973 · EI Du Pont de Nemours and Co
How Plastic Soda Bottles Are Made Stronger Using Stretched Molecules
US 4357215 · 1982
How Lithium-Ion Battery Cathodes Are Made
US 11239459 · 2022 · GM Global Technology Operations
Making Solid-State Battery Electrodes That Don't Swell and Crack
More to explore
More in Consumer Electronics
US 7657849 · 2010 · Apple Inc
How the iPhone's Slide-to-Unlock Gesture Works
US 7479949 · 2009 · Apple Inc
How Touchscreens Understand Your Finger Swipes and Scrolls
US 4528643 · 1985 · FPDC Inc
How Stores Make Custom Products On-Demand with Remote Approval
US 7469381 · 2008 · Apple Inc
How Touchscreens Show and Snap Back When You Scroll Past an Edge
New to patents?
Common Questions
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).
Same assignee
More from Corning Glass Works
Patent monitoring