The purpose of this study was to elucidate some of the factors on which accurate shade taking depends. Custom shade tabs (0.5, 1.0 and 1.5 mm porcelain thickness) were fabricated from selected Vita and Shofu porcelains. Four main factors were investigated, namely, the difference between the two types of porcelain used, the effect of light quality, the effect of porcelain thickness and the experience of the observer. The chi-square test for independence at a probability level of P <0.05 was used to analyse the results. The results indicated that in ideal light there was no difference between the two porcelains (P=0.58). The experienced observers proved better than the novice observers in ideal light conditions (P=0.003). Thickness was also significant in the overall results (P=0.0001), in that thicker samples gave more accurate results. The results indicate that in adverse light, there was an overall difference between the two porcelains (P=0.046), but no difference between the experienced and novice observers. The thickness made no difference to the experienced or the novice observer in adverse light. These results indicate that the most influential factor on shade taking was the light quality (P <0.0001); better results were obtained overall for the ideal light situation. In ideal light thicker samples gave better results (P=0.0001).