The practice of blackening characters was not printing, but it may have led to its development. Du Halde says that the Chinese printed not only on wood blocks, but on tables of “stone of a proper and particular kind.” The writing or design to be printed, while it was still wet with ink, was transferred by pressure from the paper upon which it was written to the smooth surface of a slab of stone. When the [p111] black lines of the writing or design were firmly set on the stone, the paper was peeled off. The black transferred lines were then cut out, or cut below the surface, as they are now done in the copper-plate process. The surface was inked, paper was laid on the stone, and an impression was taken. The result was, the appearance on the paper of the writing or design in white on a field of solid black. This method of cutting out the lines, so that they should appear white in the printed impression, is the simplest form of engraving. It is like that of the boy who cuts his name in the bark of a tree. He finds it easier to gouge out the letters than it is to raise them in high relief. Reasoning from probability, we should say that it should have been the earliest of the methods. Didot believes that it was known to the old Romans.[41] Du Halde says that this method of printing on stone was used chiefly for “epitaphs, pictures, trees, mountains and such like things.” He does not fix the date of its invention, but it was probably the earlier method. Didot says that he had in his [p112] library the portraits of four Chinese emperors of a dynasty which began A. D. 618, and ended during the ninth century, and also some fac-similes of the imperial writings, which were made by the same process.[42] Sir John Francis Davis, for many years British Minister to China, and author of two valuable books on that country, places the invention of block-printing in China in the tenth century of the Christian era. He attributes the discovery of the art to Foong-Taou, the Chinese minister of state, who had been greatly hindered in the discharge of his duties by his inability to procure exact copies of his writings. After many trials and failures, he dampened a written sheet of paper, and pressed it on a smooth surface of wood until he had produced a fair transfer. He then cut away every part of the surface that did not show the transferred lines, and thus produced a block in relief. The lines in relief were next brushed with ink; a sheet of paper was laid on the block, and impression was applied. The result was, a true fac-simile of his writing, and the birth of block-printing.