[As some of you know, I am a member of The Mourning Stamps and Covers Club. Here’s a piece I recently submitted to their journal, “Mourning Notes,” featuring a favorite cover from my collection of Luxembourg mourning covers.]
Secret writing with invisible ink has long been a mainstay of combatants and others to conceal messages and thereby evade postal censors. During World Wars I and II, the German postal censors used a variety of chemicals to occasionally test cards, envelopes and enclosures for invisible ink. Thus, knowledgeable postal history collectors can find covers swiped by the German censors with chemicals such as copper sulfate in their search of the wartime mails for the presence of secret writing.
The mourning cover shown above was posted from Diekirch, Luxembourg, March 30, 1943. The 12-Rpf. Hitler-head definitive pays the 20-gram letter rate to a nun at the Convent of Berthem in Berthem, Belgium, near Louvain. The sender’s surname (Hamaide) is the same as that of the addressee, so presumably the death notice was en route to a cloistered relative of the decedent.
The censor clerk, whose identification number (“22”) appears on the back, swiped the envelope with two different chemicals (referred to as “pH indicators” or “developers”). One appears as light blue swipes front and back; the other, as almost colorless swipes crossing the blue swipe on the front and running parallel to the blue swipe on the back.
The mourning cover has been opened, presumably to allow the censor to also inspect the contents. The resealing tape is tied by the censor’s red Oberkommando der Wehrmacht cancel with code letter “c.” The code letter identifies the censorship office—in this instance, Cologne, where most cross-border civilian mail sent to and from Luxembourg, Belgium, the Netherlands, and northern France was censored.
Covers such as this present intriguing questions. Why was this cover selected for chemical inspection?
- Did affixing of the 12 Rpf. Hitler-head stamp up-side-down trigger suspicion?
- Was the use of French in the address the censor’s concern? Luxembourg was occupied in May 1940; in August 1940, the occupiers banned the use of French.
- Was mail to a convent In Belgium suspicious, given the support by Catholic clergy and nuns of the Luxembourg Resistance movement?
- Were mourning covers simply more likely to be chemically censored than other types of correspondence?
Surely readers can help us learn more about this unusual mourning cover genre by contributing scans of covers in their collections that show German censorship by chemical inspection—both during World War I and World War II.
Only two other mourning covers are known that were chemically censored—one that was sent from Paris to Germany in August 1944; the other from World War I, sent from the Alsace to Switzerland in July 1915. See Gene Zhiss and Elmer Cleary, “Chemical Censorship on Mourning Covers,” Mourning Notes: Newsletter of the Mourning Stamps and Covers Club 3, no. 12 (Oct-Dec. 2009): 17-18.
To learn more about chemical censorship with many examples from Netherlands postal history, see Franklin Ennik’s fine article, “Secret Writing and Chemical Censorship of the Mails by the German Postal Authority,” Netherlands Philately: Magazine of the American Society for Netherlands Philately 36, no. 5 (July 2012): 123-137.
 Use of German stamps in Luxembourg was required beginning January 1, 1942. And In August 1942, the German authorities formally annexed Luxembourg into the Third Reich of Nazi Germany as part of the Gau Moselland.