chapter 2.2.2. Degree of coloration of liquids
This chapter now describes three methods:
- in method I (visual method), the colours are compared in diffused daylight, viewing horizontally against a white background;
- in method II (visual method), the colours are compared in diffused daylight, viewing vertically against a white background;
- method III is the instrumental method – this part of the text has been harmonised with the USP and the JP in the Pharmacopoeial Discussion Group (PDG).
Instrumental methods for measurement of colour provide more objective data than the subjective viewing of colours by a small number of individuals. With adequate maintenance and calibration, they can provide accurate, precise and consistent measurements of colour that do not drift over time. Through extensive colour-matching experiments involving human subjects with normal colour vision, distribution coefficients (weighting factors) have been established for each wavelength in the visible spectrum, giving the relative amount of stimulation of each receptor type caused by the light of that wavelength…