This way up

Take a look at a classic invert error and you may wonder how such a glaring, spectacular mistake could be made. The postal worker will always be culpable, but they may prefer to blame the error on the printing process. With many inverts the error was made as the worker passed the sheet through the printing press a second time, accidentally putting it through the wrong way up. This often creates clear errors which will be obvious to those checking the stamps produced, but with thousands upon thousands of sheets being printed, one or two examples could be missed.

And then there’s the less obvious inverts, such as the USA’s Dag Hammarskjöld invert of 1962, which to the casual observer looks just fine, but to those in the know, the yellow ink is upside down. For this particular example the US Postmaster of the time, General J. Edward Day, spoilt the fun, demanding that millions more examples of the yellow invert should be printed, commenting: ‘The Post Office Department is not running a jackpot operation.’ The episode is known by collectors as ‘Day’s Folly’. There are still a few rare examples; an invert error