What is Cornerstone?
Cornerstone is a registered trademark of De La Rue that describes a special type of watermark designed to physically strengthen the corners (and edges) of traditional ‘paper’ banknotes. De La Rue’s UK trademark for the term “Cornerstone” was filed June 27, 2006. De La Rue’s US patent application (filed in 2002) cites a British patent, dated November 26, 2001. In the US patent, DLR states that the purpose of Cornerstone is to prevent folded and bent corners of banknotes and damage to the middle of the exterior edges (tearing). They state that folded corners and middle edge damage make up a significant amount of the rejections from cash sorting machines, and can cause problems during automated handling of banknotes, such as in ATMs. Cornerstone may also extend banknote life-span by the same means (increasing the physical strength of the note in high-wear areas).
Though DLR and I have called Cornerstone a watermark, that may be somewhat misleading. Cornerstone conveys no information, nor is it an anti-counterfeiting or security feature. Its only purpose is to physically strengthen the banknote. Cornerstone simply happens to be created by the same methods as watermarks – because they are both controlled variations in the thickness of the paper – that is all.