Not all papers take ink the same way.

-----There are a variety of paper surfaces on which we print; each one reacting differently to the the viscosity of the ink and the speed at which it is transferred from the blanket cylinder. -----Coated papers accept and retain inks differently than do uncoated papers, and newsprint reacts differently yet. To accommodate these differences several factors must change; the screen frequency (sometimes referred to as screen ruling), the speed of the press, and the formulation of the inks.
-----Coated papers come in three grades; gloss, dull, and matte.

-----Gloss papers are processed more than dull coats and are heat-sealed by giant chrome cylinders. Coated sheets actually accept more ink, print more cleanly, and dry faster than either uncoated or newsprint papers. This is because the coating of these papers contains white pigments, clay, and binders that assist in the drying process and the ink sits on the surface of the paper rather then being absorbed into the paper’s fibers, allowing the air to dry it faster.

-----Dull papers also reflect light evenly off the surface and therefore produce the cleanest, sharpest results of all papers. They contain the same pigments, clay, and binders as other coated papers but are sealed with a polished, though not chrome cylinder. The drying properties are similar to gloss papers.
-----Matte coated papers are coated with a composition containing calcium carbonate as a coating pigment, a binding agent for absorption of printing ink.
Coated paper grades range from Premium to #5 and decrease in brightness accordingly. The brightness of papers is determined by the amount of bleaching that a paper receives.
-----Uncoated papers have no coating at all but can be calendared (pressed by the same type of chrome cylinders as gloss coated sheets). This calendaring process produces a glazed surface that helps ink set on the sheet.
-----Cast coated stock is a super-shiny paper produced by pressing the paper against a chrome metal drum while the coating is still wet. This paper affords superior reproduction of photographs, both in terms of color reproduction and sharp detail. The drying properties of cast coated sheets keep offset and ink transfer from happening.

-----Inks vary in viscosity from that of peanut butter for offset presses to more liquid inks for newspaper presses that are literally delivered to the press via gas station style hoses. The speed of the press and the grade of the stock determine the viscosity (and therefore, opacity) of the inks.
-----Four-color printing inks are actually translucent rather than opaque. If they were not, the blending of process (CMYK) colors would not take place. BUT, because even the Black ink is translucent, many times large, bold type printed in Black ink only can actually show the color and fiber of the paper it is printed on. To maintain the solid black appearance, a tint of Cyan ink (usually around 40%) is printed under the black to “beef it up.” To keep this tint from showing if the press miss registered, the Cyan type was shrunk in size. This can be accomplished electronically, but it is a tricky procedure.

On a related issue go to The SWOP Mystique

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