The Penny Blacks were printed from 11 plates. 10 of which are true "Penny Black Plates". The 11th plate was intended for printing in the new colour "Red Brown" and so first put to press.
As Plate 1 was not hardened, a treatment intended to decrease wear, it soon became unusable for printing. Late in May 1840 it was withdrawn from service and fully repaired and then hardened. Because of this two states are known for all the letterings, thus it is philatelically designated as Plates 1a and 1b.
Other plates underwent repairs, but only upon some impressions. Only plates 3, 4 and 7 seem never to have any repairs made. These later plates with repairs carry the 'state' designation in catalogues.
Due to a shortage of Penny stamps in the black colour, a Provisional Printing was ordered in Late January 1841. Plate 11 was cleaned and printed in Black. Over the three days of such printing, only 700 sheets were produced, making this the most scarce of the 'Black' plates.