When using sight-size, the painting or drawing is placed next to the sitter so that both appear the same size when viewed together from a given distance. In this way, shapes and proportions, colours and values can be evaluated to scale alongside nature. First documented by Roger de Piles in 1708, sight-size is primarily a portrait practice as used by Reynolds, Raeburn, Lawrence, and Sargent, but because it facilitates a direct comparison between subject and image, it is the best way to train the eye and therefore fundamental in an educational context. Students also learn to hand grind oil paint and make painting mediums, and how to stretch and prime canvas.