Cleaning gold coins and mechanical cleaning: when and how

Cleaning gold coins: when it is necessary

Gold is the most chemically inert of the metals used in coins. It does not oxidize, does not react with moisture and most acids, does not darken and does not corrode under normal conditions. That is why gold coins, having lain in the ground for millennia, often retain their original shine.

Therefore, the first rule: gold coins practically do not need cleaning. If the coin has a natural appearance and is not covered with foreign substances - do not touch it. Even minor interference can leave micro-scratches on the soft metal.

When cleaning is still necessary

• The coin was found in the ground and is covered with a crust of dirt or limescale.
• There are traces of PVC on the surface from poor-quality packaging (a characteristic sticky film).
• The coin has greasy marks from hands or other substances.

Safe methods for gold

Warm distilled water: Soak the coin for several hours. Most of the surface dirt will soften and come off without any friction. This is the safest and best first step.

Soap solution: neutral liquid soap + warm water. Soak for 30–60 minutes, then rinse. Do not rub!

Rubbish alcohol: if you need to remove PVC residues or greasy deposits - a few minutes in a 10% ammonia solution, then rinse.

What to avoid with gold: any acids (even weak ones) and mechanical friction. Although gold is chemically stable, impurities in the alloy (copper, silver) can react with acids and change the color of the surface.

Mechanical cleaning: effective and dangerous

Mechanical cleaning is the removal of dirt by physical means: using tools, brushes or abrasives. This is the most effective method for removing thick crusts of dirt, soil, limescale and dense corrosion. But at the same time, it is the most risky for the surface of the coin.

Mechanical cleaning tools

• Soft brushes: a toothbrush with soft bristles, natural hair brushes - for surface dirt after soaking. Never use hard metal brushes.
• Wooden toothpicks and bamboo sticks: are more gentle than metal, but allow you to remove dirt from the recesses of the relief. An ideal choice for soft mechanical cleaning.
• Plastic tools: plastic scrapers and stacks - less risky than metal ones.
• Metal needles and scalpels: only for experienced people! They allow you to precisely remove dense crust in problem areas, but they easily leave scratches on the metal. Used in the restoration of ancient coins under a microscope.

Safe mechanical cleaning technique

Always pre-soak the coin - it is very dangerous to remove dry dirt mechanically. After soaking, the dirt becomes softer and is removed with less pressure. Use the minimum pressure necessary. Move from the edges to the center so as not to introduce dirt into the relief. Regularly check the result under a magnifying glass.

Ultrasonic baths: contact-free cleaning

An ultrasonic bath is a device that creates ultrasonic vibrations in a liquid. These vibrations form microscopic bubbles (cavitation) that "tear off" dirt from the surface of the coin without mechanical contact. This is one of the safest methods in terms of surface damage.

Advantages: no mechanical contact, effective for small relief details, fast (5–15 minutes), suitable for most metals.

Limitations: does not remove dense corrosion and thick crusts, may be too intense for Proof coins with a mirror surface, requires a special device.

Use distilled water or special solutions for numismatic ultrasonic baths. Regular tap water contains chlorine and minerals that can leave a coating.