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The way the flash has caught the grain of this it looks like its made of two parts but its not. Walnut or come to that any quality wood with good colour and grain polished to a high enough degree will give dramatically changing effects as it is moved against the light.

To get really technical I think the laminar nature of wood produces a diffraction grating effect which varies with surface angle of incidence with the growth rings. But it disappears if you varnish it so I use a sealer well rubbed back and easily renewable wax to enhance the effect.