Measuring Textured Coatings

Textured coatings contain peaks, valleys, shadows and changing surface angles within every measurement area. Stipple, hammer tone, wrinkle, rough powder coat and orange peel can produce real reading variation even when the formulation is uniform. Repeatability comes from representing the texture rather than searching for one unusually smooth spot.

Why texture changes color readings

Texture changes how much light enters the instrument and how specular reflection is distributed. The ratio of peaks to valleys under the aperture changes from location to location. Directional textures can also respond differently when the specimen is rotated. Coating thickness and substrate may vary between peaks and valleys, adding material-color variation to the optical effect.

Choose a representative aperture

Use the largest practical aperture that fits entirely on the valid coated area and captures several repetitions of the texture. A small aperture may have excellent instrument repeatability while producing poor sample repeatability because each placement sees a different peak or valley. Record both the measurement aperture and the illuminated area where the instrument distinguishes them.

Control orientation and presentation

• Define the face, machine or spray direction and instrument orientation.
• Use a stable fixture so curved or flexible parts do not rock or deform.
• Ensure the port sits consistently without crushing high points.
• Keep edges, seams, obvious defects and damaged zones out of the aperture unless they are part of the requirement.
• Use the same SCI or SCE condition for standard and production samples.

SCI generally reduces the color effect of gloss and texture, while SCE is more sensitive to the finished appearance. Neither eliminates the need to control texture itself when texture is a specified attribute.

Build a sampling and averaging plan

Measure several independently positioned locations distributed across the part or panel. For a directional finish, specify whether each reading uses one fixed orientation or whether paired orientations are required. Report the mean, range and standard deviation. A mean alone can pass while one customer-visible zone is clearly outside the process pattern.

Establish the number of readings through a short measurement-system study: repeat without moving the sample to estimate instrument variation, then reposition between readings to estimate sample and placement variation. Increase aperture size or reading count until the result is fit for the decision.

Set color and texture acceptance separately

Use Delta E and component limits for color, then add the agreed texture, gloss or visual standard. If only color is specified, production can change texture substantially while remaining numerically acceptable in SCI. Protect against that gap with a physical appearance standard and controlled visual assessment.

Continue with powder-coated metal, glossy coatings and measurement averaging.

Last reviewed 22/09/2026 · Level: Intermediate

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