Fillers, like clay, improve opacity, brightness, smoothness and finish. Calcium carbonate reduces the acidity, or pH, in paper and thus improves paper lifetime. Alkaline papers, with low pH, are preferred for archival uses. Too much filler, however, can reduce paper strength and bulk and may dust easily in printing and converting equipment. Additives and dyes improve color or brightness.
All white papers have small amounts of red, yellow and blue dye to adjust the color of the raw pulp.
In contrast, groundwood papers, originally made with mechanically ground pulp, are more like newsprint and retain the lignin which makes paper turn yellow and brittle. Groundwood is a contaminant in recycling systems for freesheet papers because it has shorter fibers and introduces lignin. Generally, recovered paper with groundwood is downgraded for lower end-use products like corrugating medium and tissue. The new groundwood papers used in copiers and printers cannot be recycled routinely into newsprint. Moisture is always present in paper but too much can interfere with copy paper performance.