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.
Key facts
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.
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 Journey
From filing to expiry
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.
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.
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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
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