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<p>[QUOTE=&quot;The Eidolon, post: 4513321, member: 102103&quot;]Sounds like the artificial toning created a silver sulfide surface layer.</p><p><br /></p><p>The aluminum and hydroxide solution perform a redox reaction:</p><p>The aluminum is oxidized while the silver sulfide is reduced to silver metal.</p><p><a href="https://lecturedemos.chem.umass.edu/electrochemistry19_4.html" target="_blank" class="externalLink ProxyLink" data-proxy-href="https://lecturedemos.chem.umass.edu/electrochemistry19_4.html" rel="nofollow">Here&#039;s</a> someone writing a science lab for the same reaction:</p><p><br /></p><p>OXIDATION:&nbsp;&nbsp; 2 <b>Al</b>(s) + 6 OH– (aq) –––&gt; <b>Al2O3</b>(s) + 3 H2O (l) + 6 e– </p><p><br /></p><p><br /></p><p>REDUCTION:&nbsp; <b>Ag2S</b>(s) + 2 H2O (l) + 2 e–&nbsp;&nbsp; –––&gt;&nbsp;&nbsp; 2 <b>Ag</b>(s) + H2S (aq) + 2 OH– (aq)</p><p><u>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp; </u></p><p><br /></p><p>3 <b>Ag2S</b>(s) + 2 <b>Al</b>(s) + 3 H2O (l) –––&gt; 6 <b>Ag</b>(s) + 3 H2S (aq) + Al2O3(s)&nbsp;&nbsp; </p><p><br /></p><p><br /></p><p>(I just cribbed the equations from their site.&nbsp; I was never great at electrochemistry.)[/QUOTE]</p><p><br /></p>

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