Newsprint is produced at very high machine speeds, which causes the fibers of the sheet to be very directional; however, the fact that the majority of the fibers are oriented in one direction is actually an advantage from the point of view of printing, because it helps the paper take the strain of the highspeed press run, and, from the point of view of production, "runability" is the most important characteristic in newsprint. Other important characteristics include: smoothness, which is the controlling factor for halftone fineness in all direct-printing methods; softness, which is especially important in newsprint because the image carrier forces the ink into the pores of the paper during impression; opacity, which is important in all lightweight paper and particularly so in newspaper relief printing where the ink does not remain on the surface but is forced deep into the paper; and brightness, or whiteness, which is important because it contributes to good contrast between ink and paper in black-and-white printing and is of great importance in fullcolor printing.
The usual furnish for newsprint is 75 to 85% mechanical pulp, and 15 to 25% unbleached or semibleached chemical pulp.
The mechanical pulp adds the desired properties of high opacity, smooth surface, and high oil (ink) absorption, while the chemical pulp adds the necessary strength required to run the paper through fast rotary presses without breaking.
The high percentage of mechanical pulp in newsprint, which makes it very satisfactory for newspaper printing, makes it unsatisfactory from the point of view of permanence. (17 , 72 , 287 , 320 )