"Art is in everything if we choose to put it there."
Throughout his career, Knox worked and produced over 400 designs directly for Liberty of London. He was Liberty's primary designer at the height of their success and influence upon UK and International design (to the extent that in Italy, Art Nouveau was known as Stile Liberty). Knox's hundreds of designs for Liberty made his style widely known, though not his name, as Liberty kept their designers anonymous. Most of his work for Liberty was for the Tudric (pewter) and Cymric (precious metals) ranges. The gravestone of Liberty founder, Arthur Lasenby Liberty, was designed by Knox. His design talent covered a wide range of objects, ornamental and utilitarian, and included silver and pewter tea sets, jewellery, inkwells, boxes, gravestones, watercolours, graphic designs, calligraphy, a house design, fonts and even bank cheques.
After returning to teach at Kingston Art School, Knox resigned from his post as Head of Design following criticism of his teaching. About twenty of his students also quit and set up the Knox Guild of Design and Crafts. Knox was the Master of the Guild and would return to Kingston to exhibit with them. In 1913, he spent a year in the United States and, on his return to Man, acted as a censor of internees' letters during World War I. In 1919, after the War, he again took up teaching art at some of the Isle of Man's schools until his death. Knox also produced a variety of design work on the Island for publications, illuminations and gravestones.