Visualise how dust accumulation will change the appearance of a 3D object.
Dust becomes theoretically visible when the color change is ΔE > 1.5.
However, at this level, visibility needs excellent lighting and a clear contrast
with a clean area (for example, a smudge).
Research shows that most observers find a surface visibly dusty above
5% area coverage or about ΔE > 10. In practice this depends
on color, shape, texture and context.