The company Campo Rodan was one of the publishers of the First Day Covers in Belgium in that period.

A set of official First Day Covers were issued. Each cover was representing the same theme as on the stamp. At the back of the covers, a description was given about the set of stamps.

Of course, many different other cancellations with the official expo logo have been applied to a numerous number of different cachets and envelops. 

Since the 17 April was the official release of the set of stamps, some covers have the set of stamps cancelled with a day cancellation like the one below which is rare to be found:

• One of the results of the end of the WWII, was that external armies were settled down in Germany for controlling purposes. Belgium as one of the victims of the WWII, was also entitled to have some troops in Germany. These Belgian army settlements had each their own postal cancellations. They were identified through the words "Belgische Posterijen" followed by the abbreviation BPS + a number (I think from 1 to 9).

  The cover hereafter depicts a FDC cancellation of such a Belgian army settlement (date of 17 April 1958).