London, Oct 23 : Whiteness is a basic property of paper. How does it arise, and how do you measure whiteness? How difficult can it really be to produce good colour prints?

Per Edstrom of the Swedish Research Council (SRC), whose model is replacing an old model that has been used by the paper and printing industries since the 1930s, says "light that hits paper penetrates a bit. Some of it is absorbed and disappears, while some scatters in other directions."

"This is affected by fibres and fillers in the paper, and by various additives and ink. This is a rather complex process that gives paper its visual appearance," he adds.

"Tiny constituents in the paper provide the light with many surfaces to scatter against, and this helps create a lighter paper. Ink, on the other hand, absorbs light of different wavelengths, producing colour."

"The total impression is also dependent on how all of the components in the paper are distributed, for example, how the ink penetrates into the paper," he says.

Finally, the colour experience depends on how the eye and the brain interpret the visual impression, all of which means that it is not so simple to understand these phenomena in detail," says Edstrom. (IANS)