Short for post color number, it takes the absorption-to-scattering ratio k/s at 457 nm after accelerated aging, subtracts the value before aging and multiplies by 100. Working on k/s instead of raw brightness gives a fairer comparison between pulps that start at different brightness levels. Bleach plant engineers use it to judge final-stage chemistry and the effect of hexenuronic acids on brightness stability.
PC number doubled after the D2 setpoint change, so that brightness is not going to survive shipping.
Also heard as
- post color number
- post-color number
Related terms
Brightness reversion
Loss of brightness as pulp or paper yellows with age, heat or light exposure.
Kubelka-Munk theory
Two-flux light model linking a sheet's reflectance and opacity to its scattering and absorption coefficients.
Light-absorption coefficient
Per-grammage measure of how much light a paper absorbs, written k and given in square meters per kilogram.