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<p>[QUOTE=&quot;Lehigh96, post: 659569, member: 15309&quot;]Rigo,</p><p><br /></p><p>The shadow effect is real.&nbsp; However, the striking of the planchet does not cause the metal content to change.&nbsp; Rather the stresses in those areas are much higher which basically causes a localized area of the metal surface to become work hardened.&nbsp; Corrosion (oxidation/toning) occurs through process called diffusion.&nbsp; The work hardened area slows the diffusion process (corrosion) due to an increased number of dislocations in the crystalline lattice structure.</p><p><br /></p><p>And I would like to thank you for jogging my memory from my college days.&nbsp; It is not often I get a chance to employ my metallurgy degree.[/QUOTE]</p><p><br /></p>

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