The acid test for silver.

How it works

The common silver testing solution is potassium dichromate in nitric acid. On silver it forms a red compound. A drop goes on an inconspicuous spot, usually after filing through the surface, since tarnish, lacquer, and plating get in the way.

The colors

Testing-kit charts typically show:

• Bright red: fine silver.
• Darker red: sterling and 90% coin silver.
• Brown: lower-purity silver, around 800.
• Green or other colors: base metals such as nickel, brass, and copper.

The older test uses nitric acid alone: on a scratch, it turns creamy white or gray on sterling and green on copper alloys.

Its limits

• It tests one spot. On a plated piece, the result depends on whether the file went through the plating.
• It leaves a mark. The acid can etch or stain, which matters on collectible coins and fine silver.
• It's approximate. Colors are judged by eye, and the line between sterling and coin silver isn't clear.

Safety

Potassium dichromate is classified as a carcinogen, fatal if inhaled, and corrosive to skin and eyes, and nitric acid is corrosive. If you use a kit, follow its instructions with gloves, eye protection, and ventilation, or leave acid testing to a professional. You don't need to test scrap before selling it: it's paid on the silver recovered after melting.

Sources

• PubChem, potassium dichromate, hazard classification.
• Renee Newman and other jewelers on Ganoksin, identifying sterling vs nickel silver (nitric acid test).
• U.S. Patent 3,972,827, a dichromate test for silver content.

Silver tests: How to test silver · Specific gravity · XRF · Sigma verifier · Magnet · Acid · Ice · Ping · Is my silver real? · Silver stamps

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