The first essays of the art were _Skiagrams_, simple outlines of a shade, similar to those which have been introduced to vulgar use by the students and parasites of Physiognomy, under the name of Silhouettes; without any other addition of character or feature but what the profile of the object, thus delineated could afford. The next step of the art was the _Monogram_, outlines of figures without light or shade, but with some addition of the parts within the outline, and from that to the _Monochrom_, or paintings of a single colour on a plane or tablet, primed with white, and then covered with what they called punic wax, first amalgamated with a tough resinous pigment, generally of a red, sometimes dark brown, or black colour. _In_, or rather _through_ this thin inky ground, the outlines were traced with a firm but pliant style, which they called _Cestrum_; if the traced line happened to be incorrect or wrong, it was gently effaced with the finger or with a sponge, and easily replaced by a fresh one. When the whole design was settled, and no farther alteration intended, it was suffered to dry, was covered, to make it permanent, with a brown encaustic varnish, the lights were worked over again, and rendered more brilliant with a point still more delicate, according to the gradual advance from mere outlines to some indications, and at last to masses of light and shade, and from those to the superinduction of different colours, or the invention of the _Polychrom_, which by the addition of the _pencil_ to the style, raised the mezzotinto or stained drawing to a legitimate picture, and at length produced that vaunted _harmony_, the magic scale of Grecian colour.[5] If this conjecture, for it is not more, on the process of linear painting, formed on the evidence and comparison of passages always unconnected, and frequently contradictory, be founded in fact, the rapturous astonishment at the supposed momentaneous production of the Herculanean dancers and the figures on the earthern vases of the ancients, will cease; or rather, we shall no longer suffer ourselves to be deluded by palpable impossibility of execution: on a ground of levigated lime or on potters ware, no velocity or certainty attainable by human hands can conduct a full pencil with that degree of evenness equal from beginning to end with which we see those figures executed, or if it could, would ever be able to fix the line on the glassy surface without its flowing: to make the appearances we see, possible, we must have recourse to the linear process that has been described, and transfer our admiration, to the perseverance, the correctness of principle, the elegance of taste that conducted the artist's hand, without presuming to arm it with contradictory powers: the figures he drew and we admire, are not the magic produce of a winged pencil, they are the result of gradual improvement, exquisitely finished _monochroms_.