The aim of the present investigation is to find out those variables of the paper-making process that cause variation in the light transmission of paper, independently of basis weight variation. Furthermore, is intended to discover under what conditions and to what accuracy the distribution of areal mass (formation) can be characterised by the areal distribution of light transmittance. The study is carried out by measuring values of beta-ray transmission and light transmission at exactly the same points of paper samples using an aperture of 1 mm diameter and analysing the correlation of the results.
At this stage of the study the effects of furnish composition, beating, wet pressing, and calendering on the correlation between mass distribution and distribution of transmittance have been analysed. It can be seen that at least prolonged beating and heavy calendering change the distribution of transmittance in such a way that the optical formation measurement does not give a true picture of the distribution of mass.