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Have you ever wondered what luster looks like?
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<p>[QUOTE="-jeffB, post: 3335704, member: 27832"]So, I've read through this whole thread (with no regrets!), waiting for someone to call out the key difference between "luster" (from tiny parallel or radial ridges on a surface) and "shine" (from any smooth surface).</p><p><br /></p><p>That difference is that <i>luster depends on the light's <b>angle</b>.</i></p><p><i><br /></i></p><p>Or, to be more technical and precise: luster is <i>anisotropic</i> reflection, different from <i>specular</i> reflection (light reflects at the same angle it hits, as from a mirror, no matter the angle) or <i>diffuse</i> reflection (light goes off in a random direction, as from a sheet of paper, no matter the angle).</p><p><br /></p><p>On a <i>lustrous</i> surface, light hitting those grooves and ridges <i>spreads out</i> in a direction <i>perpendicular</i> to those ridges, but <i>stays together</i> in a direction <i>parallel</i> to those ridges. If the ridges spread out radially from the coin's center to its edges, you get the "wheel spokes" of "cartwheel luster" -- along the spokes, light is hitting the ridges perpendicularly, and a lot of it is bouncing into your eyes; along the dark areas, light is hitting the ridges in parallel, and nearly all of it is missing your eyes. (Or vice-versa, depending on the angle between the light, the coin, and your eyes.)</p><p><br /></p><p>Does this make sense?[/QUOTE]</p><p><br /></p>
[QUOTE="-jeffB, post: 3335704, member: 27832"]So, I've read through this whole thread (with no regrets!), waiting for someone to call out the key difference between "luster" (from tiny parallel or radial ridges on a surface) and "shine" (from any smooth surface). That difference is that [I]luster depends on the light's [B]angle[/B]. [/I] Or, to be more technical and precise: luster is [I]anisotropic[/I] reflection, different from [I]specular[/I] reflection (light reflects at the same angle it hits, as from a mirror, no matter the angle) or [I]diffuse[/I] reflection (light goes off in a random direction, as from a sheet of paper, no matter the angle). On a [I]lustrous[/I] surface, light hitting those grooves and ridges [I]spreads out[/I] in a direction [I]perpendicular[/I] to those ridges, but [I]stays together[/I] in a direction [I]parallel[/I] to those ridges. If the ridges spread out radially from the coin's center to its edges, you get the "wheel spokes" of "cartwheel luster" -- along the spokes, light is hitting the ridges perpendicularly, and a lot of it is bouncing into your eyes; along the dark areas, light is hitting the ridges in parallel, and nearly all of it is missing your eyes. (Or vice-versa, depending on the angle between the light, the coin, and your eyes.) Does this make sense?[/QUOTE]
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Have you ever wondered what luster looks like?
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