夢溪筆談·活板梦溪笔谈·活板

Printing books from carved wooden blocks was not yet widely done in the Tang. It was only after Feng Dao, Prince of Ying, first printed the Five Classics that all the classics and books which followed came out in block editions. In the Qingli years there was a commoner named Bi Sheng who went further and made movable type. His method was to carve characters in sticky clay, each as thin as the rim of a coin. Each character was a single piece of type, which was baked in a fire to harden it. First he prepared an iron plate and covered it with a mixture of pine resin, wax and paper ash. When he wanted to print, he set an iron frame on the iron plate and packed the type close together inside it. A full frame made one forme. He held it near the fire to warm it, and when the mixture had softened a little, he pressed a flat board on the surface, so that the type became as level as a whetstone. For printing only two or three copies this was not a quick method, but for printing dozens, hundreds or thousands of copies it was wonderfully fast. He usually kept two iron plates: while one was printing, type was already being set on the other. As soon as one had been printed, the second was ready. Using them in turn, the work was done in no time. For every character there were several pieces of type, and for common characters such as zhi and ye there were more than twenty each, in case a character appeared more than once on the same forme. When the type was not in use it was labelled with paper, one label for each rhyme group, and stored in wooden cases. If a rare character came up for which no type had been made, it was carved on the spot and fired over a straw fire, and was ready in a moment. He did not make the type of wood because wood grain is dense in some places and loose in others, and when wet it swells unevenly; besides, it sticks to the mixture and cannot be lifted out. Fired clay was better. When the printing was finished, the plate was warmed again to soften the mixture, and with a brush of the hand the type fell away by itself, without any trace of dirt. After Bi Sheng died, his type passed into the hands of my kinsmen, and they keep it to this day.