Separating silver from gold relies on one key principle: finding a chemical that attacks one metal but leaves the other untouched. Nitric acid dissolves silver but not gold, making it the foundation of the most common separation method. The approach you choose depends on the purity you need, the quantity you’re working with, and whether you’re refining at home or understanding an industrial process.
Why These Two Metals Are Hard to Separate
Gold and silver are often found alloyed together, whether in mined ore, old jewelry, dental scrap, or electronic waste. Both are noble metals, meaning they resist corrosion and don’t react easily with most chemicals. But silver is slightly less noble than gold, and that difference is exactly what makes separation possible. Acids that dissolve silver will leave gold sitting untouched as a dark, powdery residue.
The challenge is that when gold makes up too large a percentage of the alloy, it essentially shields the silver atoms from acid attack. The acid can’t reach the silver buried inside a gold-rich matrix. This is why nearly every separation method starts with adjusting the ratio of silver to gold before the acid step begins.
Inquartation: The Critical First Step
Inquartation means diluting the gold content of your alloy so that silver makes up at least 75% of the total. The name comes from making gold “one quarter” of the mix. You do this by melting the alloy and adding pure silver until you hit roughly a 3:1 silver-to-gold ratio.
This ratio matters. At 3:1, nitric acid reliably dissolves all the silver, leaving pure gold behind. A 2:1 ratio can work but becomes unreliable, with incomplete dissolution that leaves silver trapped in the gold. If the silver ratio is too low, the acid simply won’t penetrate the alloy, and you’ll end up with a mixed lump instead of separated metals.
To inquart, you first need to know (or estimate) the gold content of your starting material. If you have 10 grams of a 50/50 gold-silver alloy, you already have a 1:1 ratio, so you’d melt in an additional 10 grams of pure silver to reach 3:1. The alloy is then poured into water or a mold to create thin granules or a flat sheet, maximizing surface area for the acid to work on.
Acid Parting With Nitric Acid
Once inquarted, the alloy goes into a glass or ceramic vessel with dilute nitric acid, typically heated gently to speed the reaction. The acid reacts with silver to form silver nitrate, a water-soluble compound that dissolves into the liquid. Gold does not react with nitric acid and remains behind as a brown or black powder.
The process usually takes two or more acid treatments. After the first batch of acid stops reacting (you’ll notice the fizzing slows and eventually stops), you pour off the green-tinted liquid and add fresh acid. This second treatment catches any silver the first pass missed. When the acid produces no further reaction, the remaining solid is gold.
The gold residue is rinsed thoroughly with distilled water, then dried and melted into a button or bar. Depending on how carefully you controlled the process, this gold can reach purities of 99% or higher.
Recovering the Silver
The silver is now dissolved in the spent nitric acid solution as silver nitrate. To get it back as metal, you have two common options.
The simplest is copper displacement. Dropping a piece of clean copper into the solution triggers a reaction where copper dissolves and silver precipitates out as gray crystals that settle to the bottom. This works because copper is more chemically reactive than silver, so it essentially trades places. Once the solution stops producing silver crystals, you filter them out, rinse well, and melt them down.
The other option is adding ordinary table salt (sodium chloride) to the solution, which instantly converts dissolved silver nitrate into silver chloride, a white solid that crashes out of the liquid. Silver chloride then needs further processing to convert it back to metallic silver, making the copper method more straightforward for most people.
Aqua Regia: Dissolving Gold Instead
Aqua regia, a mixture of hydrochloric and nitric acid, takes the opposite approach. It dissolves gold while silver becomes insoluble silver chloride that drops out of solution as a white precipitate.
When you place a gold-silver alloy in aqua regia, the hydrochloric acid reacts with silver to form silver chloride, which is insoluble and sinks. Meanwhile, the gold dissolves into the liquid as gold chloride, giving it a vivid yellow-orange color. After filtering out the silver chloride, you recover gold from the solution by adding a chemical that forces it to precipitate. Historically, iron dissolved in hydrochloric acid (ferrous chloride) was used for this. The gold drops out as a fine brown powder, which is then washed repeatedly and melted.
Aqua regia works well when your starting material is mostly gold. But if there’s a large amount of silver, you can end up with a thick crust of silver chloride that coats the remaining metal and blocks the acid from reaching the gold underneath. This is the same shielding problem that makes inquartation necessary for nitric acid parting.
The Miller Process for Larger Scale
Industrial refineries handling large volumes of gold ore or doré bars (rough bars containing gold, silver, and other metals) often use the Miller process. Chlorine gas is bubbled through molten gold at high temperature. The key insight behind this method is that gold chloride is unstable above roughly 400°C, so in molten gold (well above that temperature), the gold itself doesn’t react. But silver, copper, and other impurities do form chlorides, which either float to the surface as a slag layer or become volatile gases captured from the furnace exhaust.
The Miller process is fast and inexpensive, producing gold at 99.5 to 99.6% purity, enough to cast into market-grade bars. Its limitations are that it can’t separate platinum from gold (their chlorides behave too similarly at high temperatures) and it doesn’t reach the highest purity levels. For that, refiners turn to electrolytic methods.
Electrolytic Refining for Maximum Purity
The Wohlwill process, used since 1908, achieves the highest gold purities available. It works like electroplating in reverse. An impure gold bar serves as one electrode (the anode), and a thin sheet of pure gold serves as the other (the cathode), both submerged in an acidic gold-containing solution. When electric current flows, gold dissolves off the impure bar and deposits as pure gold on the cathode. Silver and base metals either fall to the bottom as sludge or stay dissolved in the solution.
This process requires the starting gold to be at least 95% pure, which is why it’s almost always paired with the Miller process as a first refining step. The electrolyte solution needs a high concentration of dissolved gold to work efficiently. Under optimal conditions, electrolytic refining produces gold at 99.99% purity, the standard for investment-grade bullion.
Cupellation for Silver-Rich Alloys
Cupellation is one of the oldest separation techniques, used for centuries to recover precious metals from lead-rich ores. The alloy is melted in a shallow, porous cup made of bone ash or cement, called a cupel, inside a furnace running above 890°C. At this temperature, a blast of air oxidizes lead and base metals. Lead oxide liquefies and gets absorbed into the porous cupel, while gold and silver, which resist oxidation, remain behind as a bright bead.
Cupellation doesn’t separate gold from silver directly. It removes base metals from precious metals. The resulting bead still contains both gold and silver, so you’d follow up with acid parting or another method to split the two. Fire assayers still use cupellation routinely to determine the precious metal content of ore samples.
Safety Risks You Cannot Ignore
Every chemical method for separating gold and silver involves serious hazards. Nitric acid is highly corrosive and produces nitrogen dioxide, a poisonous reddish-brown gas that causes severe lung damage. Aqua regia is even more dangerous: it releases chlorine gas and nitric oxide, both toxic. These reactions must be performed inside a fume hood or in a well-ventilated outdoor area with the wind at your back.
Protective equipment is non-negotiable. That means acid-resistant gloves, splash goggles (not just safety glasses), and a lab coat or chemical-resistant apron. When working with volumes over 500 milliliters, gloves with extended cuffs protect your forearms from splashes. All acid work should be done in glass or chemical-resistant containers, never metal.
Spent acid solutions are classified as hazardous waste under federal environmental regulations. Solutions with a pH of 2 or below meet the legal definition of corrosive waste, and nitrate-containing solutions are classified as oxidizers. Dissolved heavy metals like lead, cadmium, or mercury in your waste can trigger additional toxicity regulations. Pouring these solutions down a drain is illegal. They must be neutralized and disposed of through a licensed hazardous waste handler.
Choosing the Right Method
For small-scale work with scrap jewelry or a few grams of mixed metal, nitric acid parting with proper inquartation is the most accessible approach. It requires no specialized electrical equipment, and the chemistry is relatively straightforward. You inquart to 3:1, dissolve the silver, recover it with copper, and melt the remaining gold.
If your material is mostly gold with small amounts of silver, aqua regia can work in a single step, dissolving the gold and dropping the silver out as a chloride. This avoids the need to add extra silver for inquartation but involves a more dangerous acid mixture and a more complex gold recovery step.
For anyone processing more than small hobby quantities, the industrial path of Miller process followed by Wohlwill electrolysis produces the cleanest results. The Miller process handles bulk impurity removal quickly, and electrolysis finishes the job at 99.99% purity. Most commercial refiners accept scrap precious metals and handle the entire process for a percentage-based fee, which is the practical choice for anyone without laboratory experience or equipment.