Luxembourg's first postage due stamps appeared on June 15, 1907, when seven denominations ranging from five centimes to one franc were issued. They remained valid until October 1, 1940, although a new design appeared in 1922, again with seven denominations; six additional denominations featuring the new design were added between 1928 and 1935.
Sole uses of each of the seven denominations comprising the 1907 postage due issue are scarce. How many do you have in your collection? What possibilities do they show?
Until 1 October 1907, the country of origin marked the short-paid amount in gold centimes on the card or letter. After that date, the UPU regulations specified that the mail item should be marked (still in gold centimes) with the amount to be collected (which was often, but not always, double the shortage). But in Luxembourg, short-paid amounts less than five centimes seem always to have been rounded up to that amount.
Here's a look at four sole-use possibilities for the lowest denomination of Luxembourg's first postage due stamps -- the 5-centime.
(i) Shortpaid incoming picture postcard from Belgium
Picture postcards with five words or less of handwriting, such as the one seen here bringing wintry holiday cheer from Brussels, Belgium, could be sent at the 5-centime printed matter rate under the preferential postal treaty between Belgium and Luxembourg. However, this postcard, posted December 26, 1909, was only franked with a Belgian one-centime definitive -- thus, marked "T" (as deficient four centimes, but the deficiency is not indicated).
Sent to Keispelt [post: Kehlen], with the 4-centime deficiency paid the next day at Kehlen [T-32 cds] with a 5-centime postage due stamp. The deficiency apparently was either not doubled or was rounded down from 8 centimes to 5 centimes.
(ii) Shortpaid incoming printed matter from Belgium sent under cross-band
Under the preferential postal treaty between Belgium and Luxembourg, printed matter weighing up to 50 g could be sent under cross-band for two centimes. Here, however, on April 9, 1913, the Peruwelz, Belgium sender posted the cross-banded printed matter franked with only a one-centime Belgian definitive -- thus, marked "T" (as deficient one-centime).
From the blue crayon marks, we see that the postal clerk has doubled the one-centime deficiency ['002'], then apparently rounded it up to five centimes ['5'], that being essentially a default minimum charge, as no smaller denomination postage due stamp existed. The 5-centime postage due stamp was canceled at Luxembourg-Ville on April 10, 1913.
(iii) World War I stampless German Fieldpost
During the World War I occupation, German fieldpost was sent stampless with the recipient paying the applicable Luxembourg domestic postal rate. Thus, fieldpost postcards were charged the actual domestic postcard rate of five centimes as postage due.
The example shown here was posted December 21, 1915, to Wiltz from the 56th Infantry Division, K. D. Feldpostexp. Censored in Trier, it reached Wiltz on December 28, 1915 (Wiltz T-33 cds). The five-centime postage due stamp is cancelled on the same day with the Wiltz II T-33 cds.
This I believe is the most common sole use of the first 5-centime postage due stamp.
(iv) Shortpaid domestic picture postcard
From July 1, 1918 to April 12, 1920, Luxembourg's domestic postcard rate was 7 1/2 centimes. The picture postcard seen here from Dommeldange addressed to Schifflange was posted January 6, 1920, franked only with a 2 1/2-centime and 4-centime Arms definitive -- thus, marked "T" (as deficient one-centime, but the deficiency is not indicated). The 5-centime postage due stamp postmarked at Schifflange, January 7, 1920, shows payment of the de facto five-centime minimum charge.