Refining silver in a workshop
Chemical purification of silver using the wet method (nitric acid).
Refining silver in a workshop is a wet acid chemical operation that is accessible but regulated. The goal is to go from an alloy (800‰ or 925‰) to 999‰ pure silver for fine jewelry or for resale as refined metal.
HNO3 (Nitric Acid) Method — most common: Both silver and copper dissolve in diluted HNO3 (50%). The resulting blue-green solution (copper nitrate + silver nitrate) is then treated with sodium chloride (NaCl): silver precipitates as AgCl (silver chloride), a filtered white powder. Drying then reduction to silver metal by electrolysis or with zinc.
Cupellation Method: Traditional assayer's technique, used for small high-precision quantities. Metal is melted with lead on a cupel (porous crucible); the lead oxidizes and is absorbed, leaving a pure silver button. Requires a muffle furnace >950°C and specialized cupels.
Expected Yield: For 100g of 800 silver refined by wet process: theoretical recovery 80g of Ag 999 − process loss (1–3%) = 77.5–79g effective. Dissolved copper is lost in effluents (partially recoverable by cementation on iron).
Safety and Regulation: Nitric acid is corrosive and produces highly toxic orange NO2 (nitrogen dioxide) vapors. Work under a certified exhaust hood. Wear coveralls, airtight glasses, and thick nitrile gloves. In Switzerland, purchases of concentrated HNO3 are regulated (OCS register). Contact your local chemist.