Correlation between the BYK's balance index and the appearance of visually assessed achromatic automotive finishes

• The inter and intra observer agreements in visual assessments were very good.
• The BYK tolerancing chart did not correlate well with visual assessments.
• The BYK tolerancing chart can be utilized as a second fine-tuning tolerancing criterion.

In the present investigation, the effectiveness of “Structure Balance Index” in correctly predicting the appearance of visually assessed achromatic automotive finishes was evaluated. For visual evaluation, the pair comparison method utilizing 16 observers assessing in a light cabinet, having a 45/0° viewing geometry, was used. The statistical results show that the observer repeatability and reproducibility were acceptable. However, evaluation of the Balance index (B) illustrates that the tolerance regions of green, yellow and red in the Balance chart of the presently prepared achromatic samples differed from the BYK's originally defined regions when compared to visual assessments. This means that this index cannot be extended to all lightness levels. Furthermore, such acceptability regions of green, yellow and red are not symmetrical enough for different lightness to promote the balance index for general use. Instead, this index can be regarded as a secondary fine-tuning corrector of Wd and LW parameters.

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