John Ruskin (1854). “On the nature of Gothic architecture: and herein of the true functions of the workman in art. Being the greater part of the 6th chapter of the 2nd vol. of 'Stones of Venice'. [48 p.].”, p.19
John Ruskin, Louisa Caroline Tuthill (1872). “The True and the Beautiful in Nature, Art, Morals, and Religion, Selected from the Works of John Ruskin”, p.408