Effect of Curvature and Surface Area on Colorimeter Readings—a Model Study

The effect of sample curvature and surface area on colorimeter color readings was determined using samples with different radii of curvature (23.5, 28.5, 36.0, and 48.5 mm) on one side and flat on other side. No curvature effect was observed with an instrument having a small aperture (8 mm, Minolta chroma meter). An effect of surface area and curvature was observed for total color difference (ΔE), lightness (L) and chroma (C) but not hue angle with an instrument having a larger aperture (91 mm, Gardner XL‐845). L and C increased with increasing surface area and radius of curvature while ΔE decreased with increasing surface area and radius of curvature. The data from this experimental work indicate that reducing the area ratio (ratio between curved and flat surface area of the text sample) to less than 1.023 by using a smaller aperture will eliminate significant effects of sample curvature on colorimeter color readings. Hue angle results were unaffected by the curvature and can be reported if the area ratio criterion cannot be met.