John Ruskin (1872). “The Political Economy of Art: Being the Substance (with Additions) of Two Lectures Delivered at Manchester, July 10th and 13th, 1857”, p.56
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.14