emco IAS Calender Blackening Tester

Calender blackening is the optical turbulent appearance of high-smoothed papers, which has a negative influence on the paper quality. The Calender blackening index measures the optical paper inhomogeneity in form of transparent parts in the paper which is caused by the calender.

Due to high local densities, especially at areas of increased basis weight as fiber crossing points, light-scattering interfaces in the paper sheet are reduced in calenders or supercalenders. One says, the fiber collapses. In incident light these transparent areas appear dark. The light is transmitted and partly reflected. This effect of “greying” of calendered paper caused the concept of blackening.

An objective assessment and quantification of the results of calendering can be achieved with the IAS module blackening. The system of Dr. Hermann Praast, Darmstadt, shows the best compliance with the subjective perception.


  • Measuring surface 10 mm x 10 mm

Calender Blackening quantities

  • Calender blackening index


  • Quality control in papermaking and paper converting industry

Technical data

Measuring field

10 mm x 10 mm

Dimensions (HxBxT)

480 mm x 360 mm x 440 mm


11 kg

Scope of supply

device with camera and illumination unit, power supply unit with mains plug, calibration strip, certificate, software, USB-Dongle, PC-ware on request

Product information

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