You can freely build on How the Float Glass Process Makes Perfectly Flat Window Panes
This patent expired in 1976. Every claim — 0 independent, 0 dependent — is now unenforceable. Anyone can use, reproduce, manufacture, sell, or offer for sale this technology without a license.
Original assignee
Pilkington Brothers Ltd
Patent granted
1959
Expired
1976
Forward citations
53
What this patent covers
The invention describes a continuous manufacturing process where molten glass is poured onto a bath of molten metal, typically tin. Because the glass is less dense than the tin, it floats and spreads out to form a perfectly flat surface. As the glass ribbon travels along the surface of the molten metal, it is cooled and solidified before being lifted off. This method produces glass with a uniform thickness and a fire-polished finish, eliminating the need for expensive mechanical grinding and polishing.
What is now free to use
All 0 claims of US 2911759 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 the production of glass using traditional rolling or drawing methods.
Does not cover the chemical composition of the glass itself, only the forming process.
Does not cover the specific equipment used for cutting or tempering the glass after it has solidified.
Who is building on this today
The process is now the global standard for flat glass production. Major manufacturers like NSG Group (which acquired Pilkington), Saint-Gobain, and AGC Inc. continue to operate and refine these float glass lines worldwide.
Products built on expired version of this technology
Modern skyscraper windows
Automotive windshields
Residential glass doors
Display glass substrates
How to cite this patent in your documentation
Pilkington Brothers Ltd. US Patent 2911759. Manufacture of flat glass. Granted 1959, expired 1976. 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.