The amount of filler in a paper. Paper consists of organic cellulose fibers combined with inorganic fillers such as clay, titanium dioxide, or calcium carbonate, added during papermaking to increase such paper properties as brightness, whiteness, or opacity. For many printing processes, a filler or ash content of 15:20% may be desirable. To determine the ash content of a paper, a sample is weighed, then subjected to complete combustion (usually at 925ºC, ± 25Cº). This removes all the organic constituents of the sample, leaving behind a residue of inorganic materials, or fillers. This is weighed, and the percentage of the original sample that remains is its ash content. Further analytical procedures can determine the chemical makeup of the ash as a means of identifying the specific fillers used.
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