The Technique of Printing _The Four Great Inventions 四大发明–活字印刷

Printing has played a very impor- tant  role  in  the  history  of civilization.  Woodblock  printing was  in  use  at  the  time  of  the Sui  Dynasty.  But  it  involved  a laborious and expensive process. Bi  Sheng  of  the  Northern  Song Dynasty  was  a  smart  printing worke r ,   a n d   h e   i n v e n t e d moveable  type  of  printing.  He carved  characters  in  reverse  on blocks of clay. When a group was finished,  the  blocks  were  baked in  a  kiln.  The  slugs  of  type  were pressed  onto  a  coating  of  rosin, wax and paper ash spread on an iron  tray,  which  was  then  heated and  cooled  to  fix  the  slugs.  If there  was  a  wrong  character,  it could easily be replaced, and the tray,  slugs  and  coating  could  be used over and over again. Bi  Sheng  laid  the  foundation for  improving  the  technique of  printing.  There  was  wooden type  in  West  Xia,  and  in  the Ming  Dynasty,  bronze  type  was invented, and later lead type was used.