This souvenir sheet, issued in 1950 to commemorate the London Internation Philatelic Exhbition, was not valid for postal purposes. Its interest to stamp collectors is for its reproductions of several classic postage stamps and for the printing process used. A planographic printing process called "collotype" that is used to produce high grade illustrations was used to reproduce the stamps illustrated in this souvenir sheet including issues of Cape of Good Hope (4 d. 185-58), Ceylon (4 d. 1857-59), Great Britain (1 d.
1840), New South Wales (1d. 1860) and Nova Scotia (1s. 1851-1853). Collotype is rarely used in the production of postage stamps.
- L.N. Williams, Fundamentals of Philately, 198.
London International Philatelic Exhibition Souvenir Sheet