THE MEASUREMENT OF DIRT IN RECYCLED FINE PAPERS

A round robin study of dirt measurements in four recycled fine papers was carried out to estimate the inter-lab variability of image analysis dirt measurements. Nine laboratories, using seven different instruments provided a TAPPI dirt count and/or a physical dirt count that included features smaller than 0.04 mm2. Good agreement was found for the TAPPI dirt count, but inclusion of smaller dirt features at higher magnification or resolution led to increasingly higher dirt counts for the paper samples. In the extreme case, physical dirt counts at high magnification gave dirt counts greater than the TAPPI dirt count by a factor of 500.