Calendering

The calender is a series of hard pressure rollers, at the end of a papermaking process (on-line) or separate from it (off-line), which is also called supercalender. The purpose of a calender is to smooth out the paper for enabling printing and writing on it, and to increase the gloss on the paper surface (papermaker call it calendering). It is understood to be a process of using pressure for embossing a smooth surface on the still rough paper surface.

source : wikipedia