The first Penny Blacks were a huge success, but soon problems became apparent.
Rowland Hill noted in his journal that some people managed to erase the cancel and reuse the stamp. The black ink of the Penny Black proved more resistant and more durable than the red ink of the cancel.
To find the ideal ink for the stamp and the cancel, trials were done in various colours. The extremely rare pieces displayed here show some of the tests done to improve the Penny Black.
= Additional information