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<p>Depiction of the Hacienda Nueva de Fresnillo during silver reduction through the patio process. The Cerro de Proaño is visible in the background. Patio process: Low grade ore was crushed and ground into powder (through animal and human power), a mercury-silver mixture was created in which silver is chemically bound to mercury (the grey circles depicted in the painting), the rock and dirt particles were washed away and the evaporation of the mercury left the silver concentrate.
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The mine and processing plant were under the control of the Zacatecas State Government and Gualdi was presumably commissioned by the state.</div>
<bdi><a href="https://en.wikipedia.org/wiki/en:Pietro_Gualdi" class="extiw" title="w:en:Pietro Gualdi"><span title="Italian-American painter">Pietro Gualdi</span></a>
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1846<div style="display: none;">date QS:P571,+1846-00-00T00:00:00Z/9</div>
<a rel="nofollow" class="external text" href="http://www.sothebys.com/es/auctions/ecatalogue/2012/latin-american-art-n08907/lot.15.html">Sotheby's</a> (includes detailed description of painting)