Cornerstone® and Edgestone™
Portals (United Kingdom)
Type: Structural watermark reinforcement features — patented paper density modifications applied during cylinder mould papermaking to physically strengthen vulnerability zones of security document substrates
Overview
Cornerstone® and Edgestone™ are a complementary pair of patented structural security paper technologies developed and manufactured by Portals Paper Ltd, a specialist high-security paper mill based in Overton, Hampshire, UK, with over 300 years of continuous papermaking heritage. Both features address the same underlying engineering problem from two different angles: the physical degradation of high-security paper documents at their most structurally vulnerable zones — corners and edges — under the demanding handling conditions of high-frequency use in security applications.
The two features are always marketed together by Portals as a combined durability system and share a single product datasheet. They are among the portfolio of Portals' patented watermark technologies, which also includes Textmark™ and Skylight™, and are produced on Portals' cylinder mould paper machines — the same equipment that produces the company's security watermarks.
Portals Paper Ltd is currently a subsidiary of Fedrigoni Group, following De La Rue's divestment of its paper operations in 2018. Cornerstone® carries a registered trademark; Edgestone™ is trademark pending or unregistered. Both technologies were developed within Portals' own R&D programme and the intellectual property resides with Portals rather than De La Rue.
Technology & Effects
Both features work through controlled, localised modification of paper density during the cylinder mould papermaking process — the same process used to create conventional multi-tonal watermarks. Rather than creating a visible image, however, Cornerstone® and Edgestone™ create structural density variations that are invisible in normal reflected light but add meaningful physical strength to the paper at the points most susceptible to wear.
Cornerstone® reduces instances of paper corner curling and folding via the addition of high density watermark rods that add structural rigidity to the paper. The high-density rods are patterns of increased fibre density deposited in the corner areas of the sheet during paper formation, creating a stiffened zone that resists the mechanical stresses that cause corners to fold back, curl, or delaminate. The rods are formed by the cylinder mould's wire design and are therefore intrinsic to the paper structure itself — they cannot be added post-manufacture and cannot be removed or separated from the sheet.
Edgestone™ helps to prevent edges from tearing by strategically increasing the thickness of the paper along the edges of the document pages. Edge tears are the other primary failure mode in high-use security documents, particularly where repeated insertion and removal from readers, scanners, and border control equipment creates stress concentrations along the page perimeter. The increased thickness zone along the edges provides additional material cross-section to resist crack initiation and propagation.
The design of the Cornerstone® and Edgestone™ features can be developed, adapted and incorporated with the watermark design. This design integration is important: both features are invisible as standalone elements under normal viewing conditions, but when designed in combination with a watermark, the reinforcement zones can be made to coincide with or complement the watermark pattern — creating a coherent substrate design where aesthetic and functional elements are unified. The Cornerstone® rods in particular are visible in transmitted light as diagonal parallel lines in the corners, which gives them a dual character: they function as a visible, recognisable substrate feature alongside their structural role.
Form Factors & Application
Both features are applied during the cylinder mould papermaking stage and are therefore intrinsic to the paper substrate itself. They are available for any paper weight and format that Portals can produce on its cylinder mould machines, and can be specified independently or together. Both are compatible with conventional watermarks, electrotypes, and the full range of printed security features applied at the banknote printing stage.
Security Levels
In the context of banknotes and security documents, Cornerstone® and Edgestone™ do not function as anti-counterfeiting features in the conventional sense — their security contribution is indirect. By extending the serviceable life of the document substrate, they reduce the window during which a degraded but genuine document might be presented alongside a counterfeit in poor condition, where wear damage makes comparison difficult. For banknotes specifically, Cornerstone® is documented extensively on De La Rue-printed issues where it is listed as a visible substrate feature in transmitted light — the diagonal corner lines being detectable by trained cashiers or sorters. The Cornerstone® pattern is also inherently difficult to simulate because it requires the cylinder mould papermaking process: photocopying, inkjet printing, or foil application cannot replicate the genuine three-dimensional fibre density variation.
Notable Deployments
Cornerstone® is documented on a wide range of circulating banknotes produced on Portals paper and printed by De La Rue, including the Bahamas dollar series (multiple denominations, 2007 series), Barbados dollar series (2007 upgrades), and Cayman Islands dollar series (2005 upgrades), in all cases listed in banknote reference literature as "Cornerstone watermarks. Printer: DE LA RUE." It has also been described in industry literature as having been first used in 2003 and as appearing in more than 200 denominations globally. Edgestone™ is positioned primarily as a passport paper feature and no specific banknote deployments are publicly documented.
- Name
- Cornerstone® and Edgestone™
- Category
- Security Feature
- Effect Types
- Corner Edge
- Company
- Product Page
- View on Supplier Site
- Linked Features
- 2 security features