Silver by Fire, Silver by Mercury: A Chemical History of Silver Refining in New Spain and Mexico, 16th to 19th Centuries


Author: Saul Guerrero
In Silver by Fire, Silver by Mercury: A Chemical History of Silver Refining in New Spain and Mexico, 16th to 19th Centuries, Saul Guerrero combines historical research with geology and chemistry to refute the current prevailing narrative of a primitive effort dominated by mercury and its copious emissions to the air. Based on quantitative historical data, visual records and geochemical fundamentals, Guerrero analyses the chemical and economic reasons why two refining processes had to share production, creating along the way major innovations in the chemical recipes, milling equipment, mercury recycling practice, and industrial architecture and operations. Their main environmental impact was lead fume and the depletion of woodlands from smelting, and the transformation of mercury into calomel during the patio process.

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Saul Guerrero is Visiting Professor of the Universidad Metropolitana, Caracas, Venezuela. He has a Ph.D. in Polymer Science from Bristol University (1980), and a Ph.D. in History from McGill University (2015). He has published articles on polymer science, oil energy policy and history.
General Series Editor’s Preface
List of Illustrations
Guide to the text


1 The genesis and nature of silver ores
Why Spain?
To have and have not
Old World silver ores
New World silver ores
A red herring
The other chemical keys
The immoveable object and the unstoppable force
The table is set

2 The dry refining process: smelting of silver ores
Deceitful mercury
Smelting of silver ores: the human context
The chemistry of smelting and the nature of the ore
The architecture of smelting in New Spain
The infrastructure of smelting in New Spain
Plata de fuego (silver by fire)

3 The dry refining process: its impact on the environment
Lead: the nature of its consumption
Lead: the directionality of its loss
Lead: its source
Charcoal and the scale of depletion of woodland
The local environmental impact of smelting
A straightforward decision

4 The wet refining process: the chemistry of the patio process
Plus ça change
The alchemy of Mercury
The gold connection
The complex mechanism of a mercury-based refining process
The correspondencia: the key to the fate of mercury
The loss of calomel
The stages in the use of mercury to refine gold and silver ores
The twists in the trail
Mercury-based refining of silver ores: the human factor
Plata de azogue (silver by mercury)

5 The physical infrastructure of the patio process
The patio process
The architecture of the patio process
The environmental impact vectors of the patio process
A unique industrial effort

6 The Hacienda Santa María de Regla
The nineteenth century
The Adventurers in the Mines of Real del Monte
The Hacienda de Regla
Main process areas
The mass balance of the silver refining processes at Regla, 1872 to 1888

7 The patio process and smelting at Regla
The keys to an efficient patio process at Regla
The challenges of the smelting process at Regla
The efficiency of extracting silver at Regla
The labour force at Regla
The mass balance for the patio process at Regla
The mass balance for smelting at Regla
The environmental loss vectors in the period 1872 to 1888
A snapshot of a refining hacienda

8 The economies of refining silver
Roads to riches
Refining costs in New Spain, as reported
The refining costs at Regla
The false positives of the patio process
Silver in the context of other commodity trades
The bottom line

9 The environmental impact of silver refining: a shift of paradigm
The base line
An estimate of the breakdown of silver production by refining process by Caja
Aggregate totals for New Spain
Aggregate totals for Mexico, 1820 to 1900
Environmental impact vectors, sixteenth to nineteenth century
What did they know and when did they know it?
Was mercury the indispensable key to silver in the New World?


Appendix A: The accounting books of Regla
Appendix B: Sensitivity matrix for refining costs
Appendix C: Estimates of silver production by Caja and refining process, including balance of mercury consumption and physical losses
Glossary of technical terms in Spanish
Archival sources
All interested in the history of the New World, Spain, Mexico, in global connections and transmission of knowledge in the Early Modern period, in environmental history, in metallurgy, and in geology.