During the early 20th century, Portals rapidly expanded its base of international customers. In 1915 the company began making paper for the Indian Rupee, then in 1921 started making banknote paper for Chile. By 1929 Portals was making paper for 41 banknote issues around the world. Building security features into its paper became a speciality of Portals. In 1940 the company pioneered the weaving of a fine security thread of special composition into its paper, a procedure that became standard industry practice.
In 1995 Portals was acquired by De La Rue, the world's largest commercial security printer and paper maker, in a deal worth £682 million.
Portals used their address “Aldgate House, London E.1” as the overprint on their stamps. At least three other companies who resided in the Aldgate House office building also used this overprint. The companies (also paper makers) were F. Keay & Co. Ltd.; Wiggins, Teape & Alex. Pirie Ltd.; and Allied Paper Merchants Ltd.
The overprints are most common on the George VI 2d stamps but are also known on SG 573. There are varieties in the style and font of the overprint.
By Mark Matlach