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<p>[QUOTE=&quot;2manybooks, post: 12292882, member: 8267&quot;]The use of alum compounds (aluminum potassium sulfate and aluminum sulfate), and their role in increasing acidity in paper, is more complex than indicated in the AI summary. The use of aluminum potassium sulfate for hardening gelatin sizing appears as early as the 16th century. A more concentrated form of aluminum sulfate became available in the 19th century. Both forms were referred to as &quot;alum&quot;. The most adverse effects appear in the 19th century, with the introduction of a mixture of alum (aluminum sulfate) and rosin used as sizing in the 1820s.</p><p><br /></p><p>This graph charts the increasing prevalence of aluminum compounds in book papers, and the corresponding drop in pH over time. (For those of us far from our chemistry classes, the pH scale runs from 1-14, 1 being highly acidic, 14 being highly alkaline, 7 being neutral.) -</p><p>[ATTACH=full]553457[/ATTACH]</p><p><a href="https://cool.culturalheritage.org/byorg/abbey/an/an17/an17-4/an17-407.html" target="_blank" class="externalLink ProxyLink" data-proxy-href="https://cool.culturalheritage.org/byorg/abbey/an/an17/an17-4/an17-407.html" rel="nofollow">https://cool.culturalheritage.org/byorg/abbey/an/an17/an17-4/an17-407.html</a></p><p><br /></p><p><a href="https://cameo.mfa.org/wiki/Alum_rosin_size" target="_blank" class="externalLink ProxyLink" data-proxy-href="https://cameo.mfa.org/wiki/Alum_rosin_size" rel="nofollow">https://cameo.mfa.org/wiki/Alum_rosin_size</a></p><p><br /></p><p>The slight improvement shown in the 20th century (which has largely continued) is due to the recognition of the problems being caused by potentially acidic additives in the papermaking processes.[/QUOTE]</p><p><br /></p>

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