The level of visible dirt present in pulp, paper or paperboard can impact its usefulness in a specific end use application. In such cases, the presence of visible dirt specks which are high in number, easily noticed in visual examination, or both, may detract more from the apparent usefulness of the paper material than does a lower number of specks, or specks which are less easily noticed by the eye. Both the number of dirt specks and their visual impact may be important. For someone controlling or monitoring the paper making process, the absolute physical area of dirt, or the number of dirt specks present in an inspection area may be of greatest importance. For the end user of the paper material, the overall visual impression may be the critical parameter.
