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<p>[QUOTE=&quot;kanga, post: 2778274, member: 9270&quot;]I&#039;ll see if I can keep this short.</p><p><br /></p><p>In 1933 for the 1928A and 1928B series the BEP was investigating the effects of relative amounts of linen and cotton (rag) content in the paper.</p><p>The experiment using a portion of the XB and YB blocks which had different relative amounts while the ZB block was the control using the then current mix.</p><p>I see nothing about the results.</p><p><br /></p><p>In 1944 a durability test was done with the SC block of the 1935A issue.</p><p>The &quot;R&quot; overprint indicated regular paper.</p><p>The &quot;S&quot; overprint indicated special paper.</p><p>Again no conclusive results.[/QUOTE]</p><p><br /></p>

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