The 2½d Prussian Blue stamp is considered one of the great philatelic errors of the 20th century. Below, and on the linked pages, is a description of how they came about, the data supporting the fact they were an error in printing, a description of the control numbers and a listing of the known postally used stamps. I have also provided a bibliography for those interested in reading the original articles. This section could not have been produced without the assistance of Andrew Claridge of Grosvenor Auctioneer and Valuers. Grosvenor very kindly made available to me scans of the various Prussian Blue and other 1935 Silver Jubilee stamps that have passed through their hands. The result is a stunning display, as you will see.

November 1934	Barnett Freedman submits colour trials of final designs. Uses turquoise-blue (prussian blue) colour on 2½d stamp.
January 17, 1935	Final imperforate set of essays submitted. Includes two colours of 2½d (ultramarine and prussian blue). King George chooses ultramarine.
March 1935	The printers, Harrisons and Sons, inadvertently print and perforate some sheets in prussian blue. All except 6 sheets destroyed.
June 24, 1935	Busy work foreman places sheets in with good stock.
June 26, 1935	Three sheets issued to Upper Edmonton Post Office (134 Fore Street). One other sheet issued to unknown post office.
July 2, 1935	A.J. Stavridi sends secretary to purchase 2½d stamps.He notices differences in colour. Contacts Stanley Gibbons Co.
July 4, 1935	Stavridi buys remaining 319 stamps from Postmaster Lewis (Lewis indicates 41 2½d stamps had been sold). Stavridi mails some of the stamps on cover to friends. Remainder eventually sold to H & A Wallace, stamp dealers.
November 1935	H.R. Harmer, auctioneer, writes to Post Office asking whether stamps were properly issued over a post office counter. Affirmative response from A.R. Kidner (Controller of Stamp Office). Remaining two sheets in stock destroyed.