ASTM E313

Optical Formula

Color coordinates from the CIE system are weighted through specific mathematical coefficients. The calculation utilizes reflectance measurements across the visible spectrum to construct the index. High values indicate a distinct yellow shift, whereas low or negative values correspond to blue or neutral tones.

Measuring both yellowness and whiteness enables a balanced assessment of optical clarifiers added to the resin.

Resin Degradation

Thermal oxidation during compounding generates chromophores that absorb blue light. This absorption produces a visible yellowing. Processors monitor this change to adjust melt temperatures.

Quality Benchmark

Datasheet values for natural resins specify maximum yellowness to guarantee aesthetic consistency. While virgin material starts with a low index, the shear in the extruder increases the value. Using recycled fractions further alters the output, requiring tighter tolerance bands than those used for virgin runs.

Correct calibration of the spectrophotometer prevents false rejections of compliant batches.