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
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