Hiding power

[3] The hiding power is measured by applying the coating to the black-and-white (occasionally gray-and-white) panels and using either the photometric or visual observation.

[3] Since the eye cannot make the quantitative assessments, yet is very sensitive to the presence of contrast, the measurements are made by varying the paint film thickness, determined by the amount of area that is coated by a certain amount of paint (so called spreading rate, typically measured in square meters per liter).

This simplified version of the radiative transfer theory reduces the paint properties to just two coefficients, one for scattering and one for absorption.

[7] The longevity of the method is due to the ease of calculating these constants using the optical reflectometry[6] (measurement of just one application of paint with incomplete hide on a black-and-white drawdown chart for each light wavelength is required).

[8] The model uses many assumptions, including the diffuse illumination, no reflections on the film/air and film/substrate interfaces, reasonable thickness of the paint layer.

[9] Historically, the measurements were made directly using devices such as the Pfund cryptometer (introduced in 1930, earlier "all-black" model is from 1919) that places wet paint into a wedge-like arrangement of plates over the black-and-white background; the wedge is moved over the boundary until the boundary line becomes invisible.

In general, the hiding power of a pigment is closely related to scattering of light by its particles while suspended in the binder.