what printing process did roy lichstensein use to create his benday dots?what process was used in newspapers?

i'm doing my a level art AR5 on pop art and would appreciate it if any one new to comment.

Some of the pictures were done with paint on canvas,while his prints were mostly Silk screen process.Some of the Benday spots were hand applied although the original process was photomechanical silk screen.Several printing methods were used commercially,Photogravure,Photlithography,