25c First Issue Postage Due
Imperforate strip of three
Mounted on black paper on card
Prifix 2007 notes that Luxembourg's first seven postage dues, issued in 1907, exist imperforate on satin paper (non dent. sur papier satiné) and are very rare.
Here is an example of this rarity, which Prifix does not price. I don't recall seeing other examples on the auction market or otherwise over the past fifty years. So, indeed, as Prifix says, they must be très rares. Who has seen the other six denominations imperforate or knows more about their history?
The 1922 Second Issue Dues
P. 13.5 horizontally
Luxembourg's second issue postage dues are listed in catalogs such as Scott as p. 12.5. However, Prifix indicates that five of the first seven second issue dues (the 5c, 10c, 20c, 30c and 50c) are also known p. 13.5 x 12.5, as are the 35c and 70c of the later-issued supplementary denominations.
So I checked several hundred examples of each of these denominations. Indeed, about every 50th to 100th example measured p. 13.5 horizontally. And, unlike the p. 12.5 examples, the vertical perforations consistently measured 12.75 (not 12.5, as listed in Prifix).
P. 13.5 x 12.75
Now to check my covers for this scarce perforation (no, I don't have hundreds of these stamps on cover!).