A frosted surface spreads reflected light. A small area that is smoother or covered by residue can reflect a more concentrated highlight and look shiny. A scratch can also catch the light, especially on a curved part. Compare the shape and direction of the mark before deciding what caused it.
Move the sample under fixed lighting
Use diffuse light first to locate the mark, then angle the part under a directional light. A broad patch with a soft or irregular outline suggests a local finish change. A narrow track that follows a direction or crosses a boundary warrants a closer look for physical damage. Either appearance can be ambiguous, so inspect under magnification and compare with an approved finish sample.
Check which production stage first shows the mark
Compare unhandled pieces and parts taken after a known handling step. An approved cleaning check on a separate piece may distinguish removable residue from a change in the surface. Keep the original part intact. Note the location, shape and light angle before investigating coating variation, abrasion or fixture contact.
Packaging sample showroom of SamBound New Material Technology Company Ltd. Company information: sambound.com.
SamBound New Material Technology Company Ltd.