Dirt count is the numerical estimation of the cleanliness of paper and paperboard in terms of the frequency of dirt, specks, or marks.
These methods for the measurement of dirt specks, residual ink particles and shives all use a similar dirt estimation chart on which dirt particles of different sizes are printed. The number and size of dirt particles are compared with the estimation sheet and reported as the equivalent black area in mm2/m2.
Dirt count is used in the assessment of tissue papers, de-inked pulps, packaging test liners and folding boxboard.
Standards and Accreditation
Smithers Pira testing is performed to Tappi T437. Other test methods include British standard and International standard BS ISO 5350 and BS EN ISO 15755, Tappi T213, T563 and T537 and DIN 54362.