This firm registered a silver mark in 1862 from Leicester Works, Leicester Street.  It advertised as a manufacturer of silver, nickel-silver, and electro-plate goods.  The brothers were William Glossop Slack (1830-1891?); George Thomas Slack (1831-1869); and Henry Walters Slack (1833-1898).  They were the sons of George Slack (c.1798-1870), a chemist and druggist in Church Street, and his wife, Jane.  The other partner in Slack Bros was George Pashley, who is more difficult to identify, but may have been born in 1830, the son of John Pashley, a joiner, and his wife, Harriet.  If so, George Pashley was a silversmith.  The only Slack brother with experience of the silver trade was Henry Walters, who was enumerated as an electro-plate apprentice in the Census (1841).  William G. Slack almost immediately withdrew from the firm; in 1865, George Thomas departed.   Henry Walters Slack and George Pashley continued trading for a few months, but were declared bankrupt in 1865.  

At the start of 1866, the assets of the ‘well-known firm’ of Slack Bros were offered for sale.  The auction included tea and coffee services, fish carvers, dish covers, and cruet and liquor frames (Sheffield Independent, 15 January 1866).  Henry Walters became a commercial traveller and eventually moved to Scotland (he was buried at West Lothian, Scotland); George Thomas became a chemist and druggist, but was again bankrupt in 1867.  In the Census (1881), William G. Slack was enumerated as a bookkeeper ‘formerly’; and in 1878 served time in Wakefield prison.  Pashley’s subsequent life is untraced.