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<p>[QUOTE=&quot;calcol, post: 3226065, member: 77639&quot;]Doug,</p><p><br /></p><p>I think you&#039;re likely right about this.&nbsp; The problem hardly exists on 19th century silver proofs.&nbsp; It&#039;s also possible that the causal mechanism is in modern planchet manufacturing and handling methods.&nbsp; Components in droplets of hydraulic fluid or lubricant may react with silver quickly, but initially invisibly.&nbsp; These initial reactants become part of the surface or subsurface metal.&nbsp; Planchet cleaning doesn&#039;t remove them.&nbsp; Later the reaction progresses to a visible stage.&nbsp; Modern hydraulic fluids and lubricants are different chemically from those used as late as the middle of the 20th century.&nbsp; They often contain silicones and synthetic hydrocarbons, detergents, anti-biologicals, etc.&nbsp; Just a theory. </p><p><br /></p><p>Cal[/QUOTE]</p><p><br /></p>

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