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<p>[QUOTE=&quot;Curtis, post: 24738588, member: 26430&quot;]My understanding it that [USER=100005]@RichardT[/USER] is correct.</p><p><br /></p><p>Everyone knows it is a chemical reaction, not a biological process. (Other fields of conservatorship have other biological disease analogies for the corrosion affecting their materials as well.)</p><p><br /></p><p>The reason ancient coin collectors (and conservators of antiquities) use a different term from verdigris is because &quot;bronze disease&quot; is both chemically and qualitatively different.</p><p><br /></p><p>I&#039;m not a chemist, but my understanding is that the verdigris reaction produces <i>copper acetate</i>.</p><p><br /></p><p>The so-called &quot;bronze disease&quot; reaction produces <i>chloride salts</i>.</p><p><br /></p><p>(I guess we could replace &quot;BD&quot; with &quot;CuCl2·3 Cu(OH)2 + 2 HCl&quot; or, for short, we could start saying&nbsp; our coins are afflicted by &quot;green cupric chloride/cupric hydroxide compound and hydrochloric acid.&quot;)</p><p><br /></p><p>Removing it from oxygen is a good start. However, it&#039;s very difficult to seal out oxygen fully enough to completely halt the process, and then it can rapidly resume. There are cases of people claiming it appeared or progressed <i>inside</i> sealed slabs. (Anecdotally, Verdicare &amp; other verdigris products don&#039;t help &quot;BD.&quot;)</p><p><br /></p><p>Qualitatively, &quot;BD&quot; / &quot;cupric chloride&quot; is so alarming because it can be a very rapid reaction and very destructive. Within weeks large portions of the coin can become powder. It isn&#039;t unheard of for it to &quot;eat&quot; holes all the way through a coin. (Even thick ones.)</p><p><br /></p><p>Here&#039;s my most recent example (first in years, happily). As far as I could tell, it sprouted in just a few weeks since I last looked at the coin. Previously there was never any visible sign of this reaction. The pits underneath are deep.</p><p><br /></p><p><i>Large photos so you can click &amp; really zoom in</i>:</p><p>[ATTACH=full]1582575[/ATTACH]</p><p><br /></p><p>I haven&#039;t seen that kind of powdery reaction product on modern coins. (And it never seems to affect fake ancients. Only ancient ancients.)</p><p><br /></p><p>There&#039;s a guy at my local coin club who brought in a plastic jewelry box full of ancient bronze coins in 2X2 holders (some cardboard flips, some rigid vinyl, some were soft types full of plasticizer). He didn&#039;t collect ancients and hadn&#039;t opened them for 20 years. (I was there giving a presentation on ancients, so people brought what they had.) Maybe 1/3 to 1/2 his coins showed some degree of active corrosion. Several had turned almost entirely to neon green-blue powder and mostly crumbled when gently probed through the plastic.</p><p><br /></p><p>For whatever reason, it only seems to affect ancient bronze that has been buried for centuries. Some people give explanations for the necessary reactions, but I don&#039;t know enough about the chemical processes to try to explain it.[/QUOTE]</p><p><br /></p>

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