The preceding remarks on pigments apply, with no difference worth noting, to colours prepared either for oil or for water-colour; which may therefore be laid on, by varying the vehicle for their proper application, to the surfaces of any of those materials which have been specified in the Second Part of this Essay, as available for different kinds of illumination. I now proceed to notice the special processes requisite in each case, commencing with those which may be best employed for vellum. This substance consists of calf-skin, carefully cleansed and scraped, and repeatedly washed in diluted sulphuric acid. The surface is rubbed down with fine pumice-stone to a smooth face, and in that condition it is fit for working upon. It is sold, prepared for use, at all the principal shops. If it has not been previously strained, or if many tints are likely to be floated over the surface, it will be well to strain it down upon a strainer or board before attempting to draw upon it. This may be done by damping the vellum, and then either gluing or nailing its edges down. When dry, it will be found to lie perfectly flat and smooth. It may be well, then, to wash it over with a dilute preparation of ox gall, to overcome any possible greasiness, and prepare it to receive colour freely. Mr. Barnard, and, I believe, other artists' colourmen, supply vellum mounted in block-books, similar to those made up of drawing-paper for sketching on; and by providing himself with one of those, the amateur may avoid the trouble of having to mount his own vellum.