Interference colorimetry of starch granules

Starch granules viewed under a polarizing microscope may exhibit vivid interference colors – how can they be measured? A tilting compensator was used to generate interference colors, they were measured by spectrophotometry (400–700 nm at 10 nm intervals), and the weighted ordinate method was used to calculate chromaticity coordinates. There was a reasonable correspondence between the subjective terms used to describe interference colors, and those used for the CIE diagram. Three different charts of interference colors were measured by fiber‐optics – only one was close to the interference colors of the tilting compensator (r = 0.805 for CIE x, and r = 0.874 for CIE y, both P < 0.005). The spectra of various interference colors were like sine waves, whereas the matching spectra from charts were irregular with occasional peaks or dips. Thus, radically different spectra shared very similar chromaticity coordinates. As anticipated from first principles, the diameter of starch granules had a strong effect on their chromaticity coordinates (from r = 0.78 to r = 0.87, all P < 0.001).