A means of measuring a paper's opacity by backing a paper sample with a black sheet of paper, measuring how much light is reflected back through the sample, then backing the sample with a thick pile of the paper to be tested and measuring how much light is reflected off the top of the backing pile and back through the sample. The ratio of these two figures is the paper sample's diffuse opacity. It is believed that the diffuse opacity method is more effective than the contrast ratio method in estimating potential show through. (See Opacity and Contrast Ratio Method.) Diffuse opacity was once called printing opacity.
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