Cleansing bath
If surface traces of grease or oxidation-related stains appear over time due to private use, these can be removed from modern coins from the 19th century using a warm cleaning bath (e.g. dishwashing detergent). It is important to ensure that the coins do not touch or even lie on top of each other during the bath. The concentration of the soap solution - ready-made cleaning baths for various coin metals are already available in specialist shops - depends on the type of metal. Old coins and copper alloys are generally most sensitive; you have to be less careful with silver and gold.
Very important : Under no circumstances mix coins of different metals in a cleaning bath. Separate bathing also applies to white (e.g. copper/nickel) and brown-yellow copper alloys (brass and bronze).
After a soaking time of around half an hour - turning the coins several times - the dirt can be carefully removed from the coins. And here the following applies in particular: the more valuable or sensitive the coin, the less pressure it requires - or even no cleaning at all. You should avoid this, especially with gold coins whose metal is relatively soft. In general, you should only remove the dirt adhering to the surface, but under no circumstances should you damage the metal of the coin!
Immersion baths for silver and other metals
The situation is different with immersion baths that are offered in specialist retailers. Due to the substances it contains, briefly dipping the coin is usually sufficient, depending on the manufacturer and instructions. They are usually used after pre-cleaning in a soap bath, are primarily directed against oxidation-related stains on new silver coins and lighten the metal. The same applies here: never use different metals in an immersion bath.
Tip: Isolated dark spots on silver coins, which indicate damage to the coin metal, can be treated with a wooden toothpick that has previously been moistened with silver dipping bath.
After treating a coin in a cleaning or dipping bath, the very important first step is to rinse it thoroughly under running water, then soak it in a bowl made of glass or porcelain (not metal), into which fresh water is preferably slowly added.
Here too, different metals may not be placed together in one bowl, nor may the coins touch each other. It is recommended to wear thin, non-slip plastic gloves while cleaning and rinsing. This means that the surfaces of the coins are not affected by sweat from the skin.
After watering there is one careful drying necessary to prevent subsequent staining caused by water droplets. It is best to first place the coins briefly between coarse absorbent paper (e.g. kitchen roll) using rubberized tweezers. It absorbs the water droplets without leaving any wiping marks.
The coins are then stored between fine, soft but lint-free blotting paper for up to half an hour. The upper layer of cloth should only be pressed lightly and under no circumstances should it be rubbed. Finally, the coins should be placed on an air-permeable surface in the warmth (e.g. over a radiator) until the last of the moisture has disappeared.
Caution: Under no circumstances should you dry the cleaned coins with a towel, as this could result in scratches caused by the finest dust particles.
Baking soda powder
An additional cleaning agent for coins is baking soda (sodium bicarbonate). The white powder, which can also be bought in drugstores and grocery stores, is well known from the effervescent powders. And it is precisely this effervescent property in contact with liquids that helps to remove additional dirt from coins.
After the first cleaning bath, the coin is placed in some baking soda. After effervescence, the treated coin must be rinsed under running water and placed in the cleaning bath a second time. This is followed by final rinsing, watering and drying (as described). Alternatively, baking soda can also be used as a sole cleaning method in a bath with lemon juice.
First, place the coin in lemon juice for about ten minutes to an hour. The acid dissolves dirt and grease without attacking the metal. The coin is then placed directly into baking soda powder, which neutralizes the acid and removes the dirt as it foams.
Here too, the coin must be carefully rinsed, watered and dried at the end. Lemon juice, as well as immersion and alternating baths, are suitable for brightening unsightly tarnished silver coins.
