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Fool’s Gold: Is Your Gold Pure or Not?


Acid test or touchstone test is a qualitative way to distinguish gold from base materials. It is a common method to check the purity of a gold sample and a standard test preferred by most pawnshops and banks due to its simple process and inexpensive tools.

Tools needed to conduct the acid test:

  • Black stone or surface
  • Nitric acid
  • Gold sample

Acid Test Procedure:

  1. The gold sample is rubbed onto a black stone. This should leave a visible gold mark on the surface.
  2. Add 2-3 drops of nitric acid on the gold mark.

Interpretation of Results:

  • An immediate reaction to the acid indicates the gold has low purity.
  • A green reaction indicates the item is a base metal or is gold-plated.
  • A cream or milk-colored reaction indicates the item is gold-plated sterling silver.
  • If there is no reaction, the item has high purity or is pure gold.

Acid Testing Safety Precautions:

Nitric acid is a colorless or yellow liquid with an acrid odor and corrosive properties. Direct skin contact may cause irritation and severe burns, while eye contact may cause permanent cornea damage. If inhaled, nitric acid causes difficulty in breathing, pulmonary edema, or corrosion of mucus membrane.

Eye irritation from chemical exposure

Chemical burns from acid contact

Due to its toxic fumes and nauseating odor, it is advised to handle nitric acid in a well-ventilated area or in a proper engineering control equipment. A ductless fume hood is suitable for acid testing as it can be easily installed in small spaces without any need for an exhaust system. This containment device is equipped with specialized carbon filters that effectively adsorb and remove acidic fumes and the acrid odor of the chemical. It also has an epoxy worktop that can withstand corrosion caused by the nitric acid.

Esco Ascent™ Max ductless fume hood offers a complete solution — from fume containment to cost-saving features.

ADC-4B_-PP with epoxy worktop

Watch the video to learn more about Esco Ductless Fume Hoods:


[1] Acid Test.

[2] Nitric acid safety tips.