Before 1840 almost no paid mail was enclosed in an envelope: mail was charged per sheet of paper, and an envelope was regarded as an additional sheet. Thanks to uniform penny postage and the principle of charging by weight, by 1855 it was estimated that 93% of domestic letters were sent in envelopes. 

A design was commissioned from the Irish artist William Mulready RA for use on lettersheets and envelopes. These became valid for postage on 6 May 1840, at the same time as the Penny Black. 

The design of the 'Mulready' was considered so fanciful it was heavily ridiculed, and these particular pre-paid envelopes did not endure. Shown left is detail of one sent by Rowland Hill shortly after the start of uniform penny postage.

However, with hindsight the Mulready design can be seen as a work of supreme 'Victoriana'  - love it or hate it, it is unmistakeably of its time.

Illustration

A 'Mulready' envelope