The 1960's was an interesting time for specialists of definitive stamps. The reason was that in this decade, postal administrations were experimenting with all kinds of different ways to speed the electronic sorting of mail. The machines used for this purpose relied on fluorescence to detect the stamp on the envelope in order to place the envelope in the correct position for the cancelling device. To this end, postal administrations introduced fluorescent papers and inks in their stamps, leading to many definitive issues of the 1960's being enormously complicated to the specialist interested in identifying all of the existing combinations of papers and inks.
Nigeria's definitive issue that appeared between 1965 and 1973 was no exception in this regard. The set featured 14 values from the halfpenny to the one pound, all featuring wildlife from Nigeria. The stamps were designed by Maurice Fievet and are truly African in their aesthetic. The initial issue which appeared between 1965 and 1966 was printed by two firms: Harrison and Sons, which printed the 1d, 2d, 3d, later 4d values, and the 9d, and Delrieu, which printed all other values and the first printings of the 4d. The stamps were also overprinted for use in Biafra during the civil war and are a subject of an entirely different, future post. The designs were as follows:
1d Elephants - the top stamp is the regular Harrison printing, while the bottom stamp bears the F.G.N. overprint. This overprint stands for "Federal Government of Nigeria" and was used for an experimental printing of official stamps that were never officially issued. Limited quantities were put on sale in late 1968. This value was also issued November 1, 1965. This stamp was also issued in booklet panes of 4 in 1966.