The reasons for the existence of the photogravure and lithographed stamps is somewhat conjectural, as the official first day cover issued in 1973 contains many of the lithographed printings. One possibility is that the Nigerian Security Printing and Minting Company was unable to obtain satisfactory results with the photogravure process, and only attempted to produce stamps using this method from January 1973 until the lithographed stamps appeared in April 1973. It is curious though that used examples of the photogravure printings can be found used as late as 1980, although this may simply reflect the fact that small Nigerian post offices simply kept their stocks on hand until sold.
The following images show the differences for all values in the set:
1. On the top stamp, there are black splotches in the background behind the cheetahs, whereas on the bottom stamp there are fine black diagonal shading lines.
2. The detailing of the shading on the log is much clearer on the bottom stamp than on the top. Now this characteristic shows a lot of variation on the lithographed stamps. On early printings, the detail is sharp and visible, but as the printing stones wore, the detail got coarser and coarser, so that the log shading is not a good guide to distinguishing lithographed from photogravure issues.
3. The imprint at the base of the bottom stamp is wider than the one on the top stamp.
1. The background colour on the bottom stamp is black, although another photogravure printing is found in dark brown.
2. The turban, the face, the hand and arm, the shirt and the pot all show more detail on the bottom stamp.
3. The imprint on the top stamp is wider than on the bottom stamp, and is printed in the yellow-green colour of the background, whereas on the lithograph it is either black or dark brown.
1. The traffic on the bottom stamp is driving on the left, and the freeway sign is narrow. On the top stamp, the traffic is driving on the right, and the freeway sign to Apapa is wider.
2. The left lane of the top stamp shows horizontal black lines across the pavement, which are missing on the bottom stamp.
3. The imprint on the top stamp is wider than the bottom stamp.
Here you have the main differences between the printings of these fascinating stamps.