This cover from United KIngdom depicts a single stamp showing the
Lomb's Silk Mill, which is part of the "Derwent Valley Mills". The Derwent Valley Mills was the birthplace of the factory system; the innovations in the valley, including the development of workers' housing – such as at Cromford – and machines such as the water frame, were important in the Industrial Revolution. The Derwent Valley Mills influenced North America and Europe. Many of the mills built in the Derwent Valley for the cotton industry survive and were reused after the decline of the industry. Some have been reused. Most of the worker's housing survives and are still in used as homes. Throughout the 1970s and 1980s, local authorities in partnership with English Heritage attempted to prevent the deterioration of the houses and mills by giving advice to owners and using grants to undertake conservation work. When the application for World Heritage Site status was made in 2000, 26 of the 838 listed buildings in the area were on English Heritage's At Risk Register and were in a state of disrepair. In 2000, the Derwent Valley Mills were nominated to become a World Heritage Site. Along with Blaenavon Industrial Landscape, New Lanark, and Saltaire (all now World Heritage Sites), the site was proposed to increase the representation of industrial archaeology on the list of World Heritage Sites. The proposal was successful and in 2001 the Derwent Valley Mills were designated a World Heritage Site.
