Texture changes the distribution of reflected light and can make the same plastic formulation appear lighter, darker or less saturated. Mould grain, spark erosion, embossing and inconsistent replication also create within-part variation. The measurement method must average the texture appropriately without hiding real production defects.
Match aperture to texture scale
The instrument’s viewed area should cover many repeats of the surface pattern. If the texture feature is large relative to the aperture, results will depend on whether the reading lands on a peak, valley or directional facet. Use the largest aperture that fits the part and verify repeatability by repositioning the sample.
Control orientation
Directional grain can produce different readings after a 90-degree rotation. Mark a datum on the part and always present it in the same direction. During method development, measure several orientations to quantify the effect; if orientation is visually relevant in service, include it in the specification rather than averaging it away.
Choose SCI or SCE deliberately
SCI reduces sensitivity to specular and surface-finish differences and is often useful for monitoring material color. SCE more closely includes the visual effect of surface gloss and texture. Neither is universally better. State which question the result answers and do not compare an SCI standard with an SCE production reading.
Separate color from texture quality
A spectrophotometer result cannot fully describe grain definition, gloss pattern or local sink and flow marks. Where appearance depends on both material color and surface replication, set separate controls: instrumental color under a fixed condition, gloss if required, and a visual assessment under controlled lighting.
Sampling plan
- Define fixed zones away from edges and severe curvature.
- Measure each zone in the specified orientation.
- Use multiple parts across the mould cavity or production interval.
- Retain individual results and range as well as the overall mean.
- Investigate cavity-to-cavity or tool-wear patterns before changing pigment.
The SD-500 and SD-700 UV provide SCI/SCE capability for portable workflows; benchtop models suit fixture-led laboratory methods. Continue with glossy plastics, injection-moulded parts and the complete guide.
Last reviewed 21/09/2026 · Level: Intermediate
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Fundamentals
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