Bon Accord Metal Detecting and Historical Society

Bon Accord Metal Detecting And Historical Society

Bon  Accord Metal Detecting and Historical Society

The Preservation and cleaning of Coins

IMPORTANT: Before using and chemicals etc make sure you are in a well ventilated room and wearing correct PPE  Goggles/Glasses and rubber gloves etc.
In not way am i liable for any damage to coins etc as this is only a guide and you follow at you own risk. Thank you.

Remember coins are worth more when the original patina is retained!!

Distilled Water   All types of coin  but may cause oxydisation over a period
One of the gentlest methods of cleaning coins is using distilled water (DW) soaks. This requires that you soak the coin for 24 hours remove the coin and gently scrub the coin with a soft toothbrush. Change the water and then repeat until the coin is clean.

Distilled water contains almost no dissolved minerals. When you put a coin in DW the minerals on the coin transfer to the water until the DW is saturated with minerals.

Soap and Water    a gentle cleaning agent used on all coin types
Soak your coins in soap and water and gently scrub the coin with a soft toothbrush. Repeat until the coin is clean.
Soap works by lowering the surface tension of water allowing the water to penetrate the dirt, by emulsifying grease, and by absorbing dirt into the foam.

Olive Oil      a gentle cleaning agent use on all coins
Place your coins in a container and cover coins completely with olive oil. Allow to soak for 1 to 6 months or longer. Change oil if it becomes discolored. After the soak period clean the coins with soap and water and gently scrub the coin with a soft toothbrush or clean mechanically if required. Repeat until the coin is clean.
NOTE: to clean the oil off of the coins a detergent specifically designed to remove oil and grease may be required. Gringgotts Coin Cleaner has been recomended. Do not use any cleaner that contains chlorine.
The oil penetrates the dirt and loosens it from the coin.

Mechanical Cleaning    all types of coins
Use brushes, toothpicks, bamboo skewers, dried rose thorns, and for the more experienced coin cleaner, battery-powered Dremel Diamond-dusted bits and dental picks to loosen and remove dirt. Work from the outer edge of the coin to the center of the coin.
Using a tool to physically dislodge or scrape the dirt off of a coin

Calgon®   a brand of washing machine descaler/softener. on bronze copper alloys only
Using a toothpick, apply Calgon® to the oxidation and encrusted spots on the coin taking care not to get the Calgon® on the patina. Let it set for a few minutes then rinse. Use a toothbrush or a toothpick to dislodge the oxidation. Repeat until the coin is clean.
Calgon® is designed to be used as a water softener with high mineral content water. Calgon® "removes" hard water minerals from water.

Ammonia   use only on silver coins and use PPE
To make your own silver coin cleaning solution, mix one part ammonia to six parts water. Soak coin in solution then gently scrub the silver coin with a small soft toothbrush to loosen dirt. Be careful not to scratch the metal. Always rinse after cleaning. Repeat until the coin is clean. Be careful not to use ammonia on silvered or fourree coins or coins with a high bronze content.
An alkaline gas composed of nitrogen and hydrogen. Aqueous solutions of with 5-10% ammonia are sold as household ammonia. Best for cleaning oily dirt.

CLR    all types of coin but be carefull
Best used as a spot application to oxidation to soften and break it up. Do not allow it to come in contact with the patina as the patina is a form of oxidation. Always rinse after cleaning. Repeat until the coin is clean. Ususally the coin is corroded under the oxidation and will have lost all detail.
CLR is a diluted acid that removes calcium, lime & rust.

Ultrasonic    use on all coins but carefully
A home or commercial ultrasonic cleaner unit is required to clean coins in this manner. Dip the coin in solution for 1-3 minutes to clean the surface of the coin. Home units are usually not powerful enough to clean heavily encrusted coins. Commercial ultrasonic cleaners can be much more effective, but may damage the surface of the coin and leave it pitted.
Ultrasonic cleaning applies intense, high-frequency sound to liquids, producing intimate mixing and powerful chemical and physical reactions. The process ("cavitation") is, in effect, "cold boiling" and results from the creation and collapse of countless microbubbles in the liquid, producing shock waves.

Formic Acid    Can be dangerous if safety precautions not taken.
A solution of 5-30 percent formic acid in de-ionized water is effective for dissolving copper compounds without affecting silver chlorides. Formic acid can also be used to brighten silver that has already been cleaned with another chemical or technique.
Cupric oxide disloves and horn silver flakes off with gentle cleaning. For the best description on how to use formic acid please refer to the following page:

Always read and follow manufacturer directions that come with any chemicals.

Tumbling      modern coins only
Using special tumbling medias such as pecan shells or stainless steel shot, the coins are mixed in and tumbled until they are clean. This process can damage ancient coins but is very good when used on modern coins that have not been subject to centuries of corrosion.
Rotary or vibratory tumbler is used to knock dirt and deposits off of the surface of the coin.

 Alkaline Glycerol   Silver and silver alloy coins only, take PPE precautions (AGRESSIVE CLEANER)

120g NaOH

40ML gycerine

1 litre Distilled water

Coins should be soaked in the solution in a glass or polythene container. this method is rapid and coin should be constantly removed for observation.

Change the solution when it becomes deeply coloured.  DO NOT LEAVE COIN IN SOLUTION FOR PRELONGED TIME

Electrolysis    Can remove or discolor the patina.  All types of coin.
Electrolysis is a very quick and efficient way of cleaning coins, unfortuantely, it will often clean the patina off the coin. Electrolysis can clean a coins so well that it will reveal pitting and scarring that may not have been visible under the dirt or patina.
Because of the dangerous chemicals given off when using salt (chlorine) as an electrolyte and stainless steel (chromium) as a cathode or annode, it is highly recomended that sodium carbonate or sodium bicarbonate (baking soda) are used instead of salt and carbon or copper conductors instead of stainless steel. You should never use any solution that contains chlorine around coins as it will damage the coin and promote bronze disease in bronze coins.

In order to make a simplest of electrolysis machines you will need a 9V battery, 2 copper wires, distilled water, and baking soda.
1. Mix one tablespoon of baking soda in about 1 pint of water.
2. Connect one copper wire to the positve (+) end of the battery and put the other end in the baking soda solution with the insulator stripped back about an inch.
3. Connect the other copper wire to the negative (-) end of the battery and wrap the other stripped end of the copper wire around the coin so that it makes a good connection to the coin.
4. Put the coin on the wire in the baking soda solution, but not touching the other wire.
5. The coin and wire should begin to bubble and the dirt and corrosion should loosen and fall off.
6. After a few minutes, remove the coin and gently clean with a paper towel.
7. Repeat if necessary.
Even the best "zapped" coin takes a lot of work, and specialty tools, to complete the "after-electrolysis" cleaning and final preservation.

To learn more about using electrolyisis to clean coins and how to make or purchase a better electrolysis setup, please visit CoinZappers

The electrolytic process requires that an electrolyte, an ionized solution (such as sodium carbonate or sodium bicarbonate in distilled water), complete an electric circuit between two electrodes. When the electrodes are connected to a source of direct current one, called the cathode, becomes negatively (-) charged while the other, called the anode, becomes positively (+) charged. The positive ions in the electrolyte will move toward the cathode and the negatively charged ions toward the anode. This migration of ions through the electrolyte constitutes the electric current in that part of the circuit. The migration of electrons into the anode, through the wiring and an electric generator, and then back to the cathode constitutes the current in the external circuit.**

For example, when electrodes are dipped into a solution of hydrogen chloride (a compound of hydrogen and chlorine) and a current is passed through it, hydrogen gas bubbles off at the cathode and chlorine at the anode. This occurs because hydrogen chloride dissociates (see dissociation ) into hydrogen ions (hydrogen atoms that have lost an electron) and chloride ions (chlorine atoms that have gained an electron) when dissolved in water. When the electrodes are connected to a source of direct current, the hydrogen ions are attracted to the cathode, where they each gain an electron, becoming hydrogen atoms again. Hydrogen atoms pair off into hydrogen molecules that bubble off as hydrogen gas. Similarly, chlorine ions are attracted to the anode, where they each give up an electron, become chlorine atoms, join in pairs, and bubble off as chlorine gas.**

Coin preservation:

The best way to preserve you coin is with Renaissance Micro-Cryystalline Wax Polish, used by the British Museum. One 200ml can will last a lifetime. Other methods include: Kiwi Neutral Shoe Polish and other waxes.

or some preservationists prefer using a chlorine free cellulose nitrate lacquer like Icralac as it stops any further deterioration

Here are some basic facts about cleaning inorganic deposits:

Inorganic deposits: For our definition, inorganic deposits are: deposits that are soluble (can be dissolved) but are not alive and did not come from a living organism.

  • Scale/lime deposits
  • Rust, Corrosion and Oxidation
  • Minerals and Rock Formations

The most common way to clean inorganic deposits require acidic cleaners. Acidic cleaners: lemon juice, vinegar, club soda, ketchup, fats and oils (sunflower oil, lard, olive oil...etc)

The trick is to clean the unwanted inorganic deposits while saving the patina (which is a form of oxidation).

We know that there are many more methods and new ones being discovered every day. If you have any cleaning methods you would like to share, please share by usinfg form submisstion

**Definition of electrolysis from

Always read and follow manufacturer directions that come with any chemicals


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