Effects of colour measuring mode and light source on the colour of shade guides.

The objectives of this paper were to evaluate the effects of colour measuring modes [specular component excluded (SCE) versus specular component included (SCI)] and the standard light source (C, A or D65) on the colour of shade guides. After the labial part of shade tabs of two shade guides (Vita and Chromascop) was polished flat up to no. 2400 silicone carbide paper, the colour was measured according to the International Commission on Illumination (CIE)L*a*b* colour scale on a spectrophotometer. In both shade guides, all the average CIE L* values of each shade series, and most of CIE b* values were different depending on the measuring mode (P < 0.01). However, there was no difference in CIE a* values depending on the measuring mode. Colour difference (deltaE*) between the values measured with SCE mode and with SCI mode was 3.21-6.50 in Vita shade guide, 3.22-5.47 in Chromascop shade guide. DeltaE* caused by the difference in light source was very small in Vita shade guide regardless of the measuring mode. In the Vita shade guide, the shade series (A-D) was negatively correlated with CIE L* and CIE a* values measured with SCE mode. In the Chromascop shade guide, the shade series (100-500) was negatively correlated with CIE L* value measured with SCI mode.