A lot of classic philatelic ground already has been tilled, but the post-WWII era has hardly been touched. In building a comprehensive collection of Luxembourg postal history, postal historians particularly should not overlook commercial uses of the definitive, postage due, commemorative, and semi-postal issues during the period from 1945 up to 1960, when the fifth Charlotte definitive issue appeared. These can be just as challenging as collecting the classics.
For example, consider the five-denomination stamps-on-stamps set shown above, which was issued on May 24, 1952, in a quantity of only 37,416 sets for the Centilux Philatelic Exhibition.. These stamps were only valid for postal use until December 31, 1953—a period of just 586 days. The 8-franc and 10-franc denominations were sold at the Exhibition for an additional 20 francs as part of the admission price. Commercial covers using the two high values are seldom seen, which is not suprising given how contrived their sale was. The three lower values (80¢, 2.50 fr. and 4 fr.), however, were sold at face value and did see some limited commercial use, as shown below. Technically, these are airmail stamps (they are inscribed POSTE AÉRIENNE) and Prifix lists them as such, although they were routinely accepted for and seem designed to serve the then-current surface rates. In addition to covers, Prifix lists five plate varieties for this set, which you also might want to include in your collection.
The five-stamp set posted from the Centilux Exhibition on May 30, 1952, by registered airmail to Bourbon-l'Archambault, France, and received there on June 3, 1952.
Picture postcards, both posted to Germany on
May 29, 1952, from individuals who attended the exhibition. The card on the left shows the 29th of May exhibition cancel; the card below shows the Luxembourg-Ville [J] postcancel on that date. The 2.50-franc Centilux airmail pays the postcard rate.
A 22 g cover charged at the UPU rate of 4 francs for the first 20 g and an additional 2.50 francs for the second 20 g or fraction thereof, posted on August 26, 1952 from the Clervaux [tourist cancel] to Rome, Italy, August 28, 1952, with the 6.50-franc postage paid by a combination of Centilux airmails and Charlotte definitives.
A domestic cover from Luxembourg-Gare, May 18, 1953, to Clausen, franked with a pair of the 80-centime Centilux airmail and a 40-centime Charlotte definitive to pay the two-franc domestic letter rate.