The National Archive of Venice contains some documents pertaining to Muranese glassworkers who traveled to England, beginning in 1620. These craftsmen instructed English glassworkers, and the rise of the local glass industry eventually led to a ban on imports of glass from Venice. However, as reported by the Venetian ambassadors in London, glass made in England was more expensive and less refined, and it also required the use of considerable quantities of wood, which was not abundant. Producers such as Sir Robert Mansell and the duke of Buckingham turned their attention to the manufacture of sheets of glass for mirrors, which they could make easily and inexpensively. They could save additional money by importing such sheets from Muranese glassworkers. These exchanges were forbidden by Venetian law, but glassworkers often evaded the restrictions. Glassworkers from Altare (in addition to those from Venice) went to work in England as George Ravenscroft began his production of flint glass.