Calculated from the same Kubelka-Munk inputs as the scattering coefficient, it captures lignin, dyes, dirt and ink particles that soak up light instead of redirecting it. Fully bleached chemical pulps sit well below 1 m2/kg at 457 nm, while unbleached and mechanical pulps run ten or more times higher. Raising k adds opacity but always costs brightness, which is why black or gray dye is a last-resort opacity fix.
Absorption coefficient doubled on the recycled line, so the deink plant is letting ink particles through.
Also heard as
- absorption coefficient
- k
Related terms
Light-scattering coefficient
Per-grammage measure of how strongly a paper redirects light, written s and given in square meters per kilogram.
Kubelka-Munk theory
Two-flux light model linking a sheet's reflectance and opacity to its scattering and absorption coefficients.
Brightness
The blue-light reflectance of pulp or paper, read at an effective wavelength of 457 nm and reported as a percentage.
PC number
Post color number: a Kubelka-Munk measure of how much a pulp yellows during an aging test.