Know one's nuances...
This post is more about stamps than postal history, but illustrates what can be found unexpectedly when you know certain nuances, so to speak.
Both these French covers were mailed by the "Gallien & Toupet" private bank in Granville, Manche, in the early 1850s. The top cover bears a 20 centime black Cérès stamp, the first postage stamp issued in France on the 1st of January 1949. Although the stamp can be bought in average condition for as low as five euros, the catalogue value is around 50 euros for a nicely used example with four margins (early stamps were not perforated so had to be cut from sheets by the staff in post offcies... often with horrible results as far as stamp collectors are concerned). This, incidentally, is far, far lower than prices asked for the Great Britain “Penny Black” which, numerically, had around 77 million copies issued, more than twice the first 20c French stamp... but it was recognised as the world's first postage stamp.
However, the 20c Cérès stamp printings were made on different shades of paper, the ‘standard’ one being on slightly yellowed. Later printings were on white, light fawn or light buff, deep fawn/buff, tawny fawn, ivory; and then there were differences in the shades of black... so a potential minefield for casual collectors!
The example illustrated here was purchased as a ‘standard’ colour printing, but is in fact the chamois foncé shade catalogued at 625 euros on cover, or more than five times the normal because of its scarcity (I have only seen two others on covers listed in auctions).
The lower cover is franked with the 25 centime blue Cérès (although on the same type and weight of letter, the tariff was raised to 25c on the 1st of July 1850... so the 20c black only had a short life of 18 months, adding to its scarcity. As with the GB Penny Black, it was found that the black colour enabled postmarks to be easily erased and stamps to be fraudulently used again, so the issued colours were soon changed.
The 25c Cérès blue stamp is neither common nor scarce (45,218,100 were printed, and of course many millions were thrown away before collecting became popular) but again it had a short life of about 18 months because Napoleon III ‘headed’ the stamps of the République from late 1852. What makes this 25c Cérès stamp valuable, though, is a printing flaw. Although it has been affixed to the cover inverted, a mis-printed ‘circle’ can be clearly seen behind the lower hairline of the head. This flaw is called an ’anneau-lune’ or ‘moon ring’ and is due to a piece of grit or bubble in the ink temporarily stuck to the printing plate. In this case it adds more than 250 euros to the already good value of the stamp on a cover!
So it pays to know your nuances... certainly of colour. Not unsurprisingly, printing flaws are not so collectible, though technically scarcer, and few catalogues mention them. They rarely occur nowadays with modern printing presses, and those from bygone days would have been thrown away as not being perfect!