Cleaning (restoration) of found ancient coins. Copper and Silver. Bronze and aluminium. Ways to clean coins without leaving your home Restoration of copper coins

Cleaning of coins is one of the responsible types of restoration, it is important for their study, dating, identification and storage.

Ancient coins made of silver and copper alloys, found in hoards or other archaeological excavations, most often come to the restoration workshop heavily corroded, and sometimes completely mineralized.

Under the influence of water and salts, copper is destroyed in the soil with the formation of green carbonates and chlorides, red copper oxide and black oxide. Compounds of tin and lead are found in the corrosion layers on bronze coins. Silver-copper alloy coins are often coated with copper corrosion products.

Sometimes silver under the action of chloride salts turns into gray-violet chloride - horn silver. In air, copper alloys darken from oxidation, and silver - as a result of the formation of sulfide.

The restorer must be very careful about the restoration of numismatic monuments. In particular, it is necessary to make the right choice of the reagent necessary for cleaning from corrosion, since a reagent that is successfully used for some coins may be unsuitable for others, i.e., it will lead to their destruction or to serious distortions of their appearance. It is desirable to achieve and preserve the "noble patina" - a kind of certificate of antiquity of objects.

When starting to clean coins, you should first of all find out: what metal they are made of, whether they have a metal core, to what extent it has been preserved, what salts the coins are covered with.

It is important, for example, to determine the presence of copper chloride in corrosion crusts on copper coins, which in humid atmospheric conditions causes an active corrosion process - "bronze disease".
To detect copper chloride, a humidification chamber of a simple device is used: a glass vessel is filled with water by about 1/3 of the volume; a perforated (perforated) plate made of plastic, plexiglass or porcelain is placed above the water, on which coins with a corrosive layer are placed. The container is tightly closed with a lid. In this state, it is left for 1-3 days.

In addition, the presence of coins in the chamber contributes to the loosening of the surface layer of oxides, facilitating further cleaning operations. If there is copper chloride in the corrosion layer, then droplets of liquid, colorless or slightly greenish, will necessarily appear on the surface of the coins. Otherwise, the droplets do not come out: copper carbonate, nitrous oxide and copper oxide are stable in humid conditions (note that horn silver on silver coins is also stable). If copper chloride is found, it must be removed from the deepest pores and very thoroughly.

Often, in archaeological excavations, coins are found “boiled”, i.e., forming a shapeless mass due to the oxides connecting them. We do not recommend separating such coins by heating them and lowering them into cold water. sodium hydroxide solution and heat up to 30-50 °. After that, the coins can be separated from each other, determine the condition of each of them and start cleaning.

The main ways of clearing coins are mechanical, chemical and electrochemical. During restoration, a combination of the mechanical method with others is most often practiced.

Machining consists in removing surface layers: earth, sand and individual corrosion bumps. It is produced using various brushes (bristle, brass and glass fiber), scalpels and dental burs of various sizes. However, these tools must be used with great care. With inept and rough use, they are easy to scratch, which to some extent distort the inscription, images, etc. Chemically, in combination with a mechanical method, coins are cleaned, covered with a thick layer of corrosion products, but retaining a metal base, as well as coins from gold and silver.

To remove a cherry-red coating of cuprous oxide from copper coins, you should lower the coins into a 5-15% ammonia solution, but so that they are completely immersed in the solution, because in contact with air, the effect of ammonia on the metal is destructive. Instead of ammonia, you can successfully use a 5-10% solution of ammonium carbonate, which is less aggressive towards copper and bronze. If copper coins are covered with salts consisting of copper carbonate (dark green), these deposits should be removed with a 5-10% citric acid solution. It slowly dissolves copper salts and oxides and does not dissolve metallic copper.

There are also copper coins covered with a yellowish-pale coating of lead carbonate. This suggests that either there is a lot of lead in the alloy of the coins themselves, or they were lying in the ground with lead objects. To remove such plaque, a 10% solution of acetic acid should be used, which easily dissolves lead carbonate.

Sodium hexametaphosphate (G.M.F.N.) can serve as a “softener” for corrosion layers on copper coins. It is a vitreous, highly soluble salt. It must be dissolved with continuous stirring, since the vitreous mass sticks to the bottom of the vessel. M.F.N. is used in the form of a 5-20% solution.In a cold state, it acts slowly.To speed up the process, it is necessary to heat the solution to 60-80 °.

G.M.F.N. absolutely safe for metal and due to the slow action allows you to easily follow the progress of cleaning and use mechanical processing in a timely manner.

The restorer often has to deal with coins that are completely mineralized, which are not always possible not only to open, but also to save. The success of the treatment depends to a large extent on which copper compounds have replaced the metal as a result of complex mineralization processes. First, you should carefully, without physical stress, remove surface layers. If in this way it is possible to reveal one or another ornament, inscription, etc., then this should be limited. If mechanical processing has not "opened" the coin, a 5% solution of caustic soda or ammonium carbonate is used.

Taking into account that the degree of preservation of coins submitted for restoration is different, it is difficult to give definite recommendations regarding the time of their residence in one or another reagent. Therefore, periodically removing the coins from the solution, you should gradually remove the softened layers by mechanical means, thus contributing to the acceleration of the clearing process.

Cleaning of silver coins is carried out mainly in a chemical way. Such cleaning is reduced to the removal from the surface of oxides and salts of other metals, mainly copper compounds. Copper compounds on silver coins are recognized by their green color. To remove them, you need to put the coin in a glass vessel or in a porcelain evaporating cup and pour 5% sulfuric acid solution. To speed up the process, it is possible to carry out cleaning with heated solution, from time to time removing the coin, rinsing with water (preferably running water), then cleaning the mechanically softened salts with brushes - bristle or glass fiber.

With repeated operations of this kind, the layers gradually decrease and completely disappear. You can also use a 5-10% solution of formic acid (preferably heated to 50-70 °). It softens well and removes oxides and carbonic compounds of copper on silver. The hotter the solution, the stronger its effect. The formations of violet-gray horn silver are exceptionally soft. Such coins often lack a metal core, and the possibility of their complete loss cannot be ruled out during cleaning. But if the crust of horn silver is not too thick, the coin can be immersed in a 5-10% solution of ammonia or ammonium chloride. In these solutions, horn silver softens, after which it is carefully removed mechanically.

For coins that have retained a metal core, but have very dense, hard, "thick" oxides, as well as fragile coins, the method of electrochemical reduction can be applied. This method does not require special equipment. Zinc and aluminum are usually used for electrochemical processes.

Practice has shown that for cleaning coins it is best to use plates made of sheet zinc or aluminum, with holes punched into them (like a grater). As an electrolyte, caustic soda or formic acid of 5-10% concentration is taken. At the bottom of the glass vessel (the recovery process is clearly visible in it), the mentioned zinc or aluminum plate is placed. Several coins are laid out one to the other on the "gritty" surface of the plate, which are covered with the "gritty" surface of another similar plate. After that, the vessel is filled with the prepared solution so that the coins with the plates are completely hidden.

Processing in this way should be carried out with particular care and caution, with frequent monitoring of the progress of the process. Mechanically removing the restored and softened corrosion products, they examine the coin through a magnifying glass to determine the degree of its clearing. After inspection, if necessary for a clearer identification of the image, it is again subjected to electrochemical processing.

Note that gold and "new" coins that have not been in the ground, but have only been in circulation for a long time, are cleaned easily and quickly. Fatty substances must be removed from them with acetone, gasoline or alcohol and lowered into a 5-10% sulfuric solution. , citric or formic acid.

After cleaning the coins in one way or another, they should be thoroughly washed (“digested”) in several changes of boiling distilled water until the water is neutral according to the universal indicator and soluble chlorides are completely removed: the cooled sample of the last wash water should not become cloudy from the introduction of a drop of 1.7 % solution of silver nitrate.

After washing, the coins are dried in acetone, then in alcohol for 30-60 minutes. For this purpose, you can also use a thermostat (special drying cabinet), keeping coins in it for no more than two hours at a temperature not exceeding 100 ° C.

Copper coins that showed signs of bronze disease are again placed in the humidification chamber after cleaning. If drops of copper chloride appear in some places, these pockets are carefully cleaned mechanically, and the coins are “boiled” again.

If copper coins have an unpleasant sheen after cleaning, a light to dark brown patina can be artificially created. To do this, you need to take 50 g of copper sulfate and 5 g of potassium permanganate per liter of distilled water. In the prepared solution, heated to 70-80 °, lower the coins and hold until the desired shade is obtained.

After drying, the coins must be preserved with a protective coating - paraffin or synthetic resins. For this, 5% solutions of polybutyl methacrylate in acetone, toluene or xylene and polyvinyl butyral in alcohol or a mixture of alcohol and benzene (1: 1) can be recommended.

After conservation, it is necessary to store the coins not in “heaps”, but in separate boxes or trays with compartments. In this form, they will not touch and better retain their protective coating. In addition, when examining restored coins, it will be easier to identify those on which corrosion has reappeared.

How to clean a coin

Coins are made of platinum, palladium, gold, silver, copper, bronze, nickel, iron, zinc, aluminum, porcelain, etc. Coins are minted specifically for collectors using the "proof" technology and for circulation and collectors, but with simple quality. Methods cleanings are: mechanical, chemical and ultrasound. Mechanical include: rubbing against felt (such as an old felt boot), cleaning with sand, GOI paste, tooth powder and other abrasives. The dirt may be removed, but the coin will be hopelessly ruined.

So I won't even consider it. The reasons for the desire to clean are: "touched with greasy fingers", ugly patina, the appearance of oxides on the coin, which should not have them, dirt, corrosion. Now for each case in more detail.

Coins made of platinum and palladium generally do not need to be cleaned. If these are coins for collectors minted using the "proof" technology, then it is enough to rinse under warm water (but not the one that flows from the tap, but buy drinking water and heat it. Chlorinated water under the tap and chlorine can settle on the coin between small fragments of the image, and from there you can already get it out of Fig. Refers to all coins "proof" !!!). Further attention! Coin drying applies to coins of all materials!

Do not blot with a towel. You should buy a good three-layer toilet paper or a paper towel for hands, unwind a piece, fold it in half and, putting it on one half and covering the other half on top, gently blot. The coin will dry and not be scratched. Alternatively, you can dry it with a hair dryer, but this is more difficult.

It is enough to wash palladium and platinum not in "proof" with soapy water. Further on the upper scheme drying.
Gold coins - any quality. There is subtlety here. Sometimes there are black dots on the field of the coin. It's not always dirt or something else. It can also be pieces of slag that have fallen into the melt, and then, during the rolling of the sheet, crawled out to the surface. There is no way to remove them - they are in the body of the coin itself. It is better to buy a good one right away. This happens on the Russian 25 rubles of the "Signs of the Zodiac" series and on the "Russian Ballet" series of 1991. But if the "zodiac" can be found good, then the "ballet" is almost unrealistic. If it's fingers - then just soapy water. And better - Reinigungsbad from Delu. Or at worst Reinigungsbad from Leuchtturm.

Surface pollution removes perfectly both. Gold royal chervonets and similar coins (both in Russia, and France, and Austria, etc.) are cleaned in the same way if Glanzcreme from Silbo is not at hand. And most likely it is not at hand - it is not for sale yet, but is going through the testing stage. It is a jar of 40 ml with a turquoise cream. Not only does it remove grease, it also removes the yellow-brown patina (copper oxide) and gives the coin a shine.

Proof-quality silver coins with a silver content of 80% or more can be washed with Leuchtturm's Reinigungsbad. In principle, this is sufficient. Drying - see above. But you should not buy such coins if you are not confident in your experience. Here is one of two things - you can buy a heavily lapped coin, clean it and see that it is ideal, or vice versa - buy it with a light imprint, wash it and find scratches. It should not be forgotten that silver - especially high-grade - is a soft material.

Coins not for collectors of silver. It's easier with them. If this is high-grade silver - above 80%, then the easiest thing is to go to the pharmacy and buy ammonia. Better, of course, ammonia, but pharmacies do not have it. Put a coin for 3 minutes and then rinse. Silver mirror reaction - everyone remembers school chemistry? You can also use Reinigungsbad from Leuchtturm. Leuchtturm produces liquids for cleaning silver, gold, copper. But it only removes surface contamination.

If silver is less than 80%, then it makes sense to take Trilon B. You can find it with friends who work in chemical industries. A saturated solution is made (water-1 glass is brought to a boil, poured into a glass, and then Trilon B is poured into it (you can buy it here) until it stops dissolving. Naturally, you need to mix it.), A coin is lowered there by the same 3 -4 minutes (or more - depending on the degree of contamination), washed, dried - and in the album. A big plus of Trilon B is that it is absolutely harmless to humans - and even useful. It is used to remove heavy metals from the body. The taste is similar to lemon - with sourness.

For non-collector silver and gold, ultrasonic cleaning can be used. In Germany, there is a company that produces such devices. It consists of a bath about 30 * 15 * 10 cm and an on / off button. A special liquid is poured into the bath, the machine is turned on and the process has started. The downside is that only light dirt can be cleaned. When cleaning a corroded coin, it can all turn into dust - I personally saw this. Yes, and the teeth hurt during the operation of the machine. Well, at least the seals do not fly out. And the liquid will have to be bought in addition.

A method for cleaning silver coins of any samples was sent by a colleague. Buy a battery electrolyte, put it in it for a couple of minutes, then rinse with water, then wipe it with a cloth and rinse again with water. Haven't tried it myself. Perhaps it is precisely because of the mechanical effect (with a cloth) that it is effective.

Coins made of bronze, copper, brass are perfectly cleaned by Reinigungsbad from Leuchtturm. Better, of course, from Silbo, but it is more difficult to buy. You can try to boil royal copper in used engine oil. The greens really clean up. But do not forget about safety. You can try Trilon B.

Coins made of aluminium, zinc, iron should be cleaned only by Reinigungsbad from Silbo. All other home-grown remedies will not give the desired effect. Before cleaning, you need to carefully examine the coin - will it hurt it? There are caverns hidden under a layer of oxides - such coins spoil the collection. These are royal copper and French colonial coins of the 1920s.

Nickel coins both in "proof" and for circulation are easy to clean - wash with soap and water. You can also use plain water. It is more difficult if copper is used as a ligature. Then - Reinigungsbad from Leuchtturm.

Coin storage

There are several ways to store coins.
First way. The collection is placed on wooden or cardboard tablets, divided into nests. This makes it possible to review all the material at once and, if necessary, take each of the coins in hand.
The second way. The collection material is stored in albums (munztash) with pockets, which are made of elastic, colorless and transparent plastics.

The third way. Coins are placed in cardboard tablets with round through holes into which coins are inserted. They are held due to the adhesion of the rib to the surface. Transparent cases made of plexiglass, made handicraft, are known. At first glance, they attract the attention of collectors, but they are not very convenient to use. In places of contact with metal, the material of the pencil case rubs, fades, and quickly loses its transparency.

In all cases, the collection material must be stored in a dry place, protected from dust and moisture.
It is recommended to take coins not by the field, but by the edge. Carelessly picked up coins, before putting them back into storage, must be washed with warm water and soap and dried.

No matter how unexpected it sounds - do not be surprised: a coin only for a collector is a coin. For the plant that produced it, these are products, the manufacture, storage and movement of which are subject to certain requirements, rules and, if you like, traditions. This is what I would like to talk about...
A novice numismatist approached the editorial office of "Miniature" and, complaining about the lack of literature "on the technique of collecting", asked him to consult on the possible causes of the appearance of traces of corrosion on commemorative proof coins, and ways to prevent and "treat" such "diseases".

1. Keep coins of improved quality (proof, proof-flake) in dry rooms, with a relative humidity of no more than 80%, at a temperature of 15 to 40 degrees (C). It is advisable not to violate the original packaging, but if necessary, inspect a "live" coin, it is advisable to take it only by the side surface (edge) with soft-tipped tweezers, or with gloves (preferably rubber).

2. Factory packaging of coins is of two types: in a film (polyethylene-cellophane) and in plastic capsules with subsequent sealing in a film. In no case is it recommended to store collectible coins in albums without factory packaging: this is a direct way to degrade their quality. If you got a coin without packaging - do not despair. Being careful, you can brew it in a plastic bag, and finally, purchase a capsule of the appropriate diameter to limit the impact of the external environment. For long-term storage, in the absence of special furniture, it is best to use cardboard boxes with a lid, in which to place coins in one row.

3. When cleaning coins periodically, use alcohol or acetone. Do not use chemicals suitable for normal quality coins that are dirty or corroded. Polished backgrounds and matt reliefs are very sensitive to such chemicals and can be damaged as a result. In general, in each specific case of cleaning coins, you should seek advice from more experienced colleagues. Acquaintance with special literature will not hurt either.

Unfortunately, the literature abundantly entering the numismatic market really suffers from a lack of information and practical recommendations on such an important issue as collecting methods, methods of preserving and preserving material, and cleaning coins. Meanwhile, every collector should have certain knowledge and skills in this area, based on the centuries-old practice of their predecessors. Goznak enterprises that produce such specific products as "numismatic coins" have not prepared appropriate instructions, such as those that certainly accompany household goods. Such a "reminder" would not only help numismatists, but also make trading organizations take their business more responsibly.

Just as a medal has a reverse side, a coin, in addition to a purely external perception, leaves an impression as a product made using the most complex technical devices, a product whose certain level of quality is determined by the standards. And here, none of her artistic merits can compensate for the disappointment when a marriage is discovered. Even with modern methods of quality control, the main one remains visual, and it depends on the visual acuity of a person, multiplied by his experience. That is, to a greater extent, from the subjective characteristics and capabilities of a particular employee.

Technical devices at this stage of the coin process have not yet been invented. And this is the objective reason for the appearance of marriage, on store shelves and in collections of collectors.
But are mints always to blame for the fact that their products are "sick"? Especially if they are not provided with proper handling and storage conditions. The answer is obvious: not always. And the point here is not at all the absence of special literature (it does exist!) Or accompanying instructions. Often collectors themselves do not attach much importance to this issue, "working" with numismatic material.

Inaccurately opened packaging (film, capsule), careless manipulations with coins (without gloves or tweezers), and finally, unfavorable, usually completely unprepared storage conditions for the collection - all this leads over time to a decrease in the safety of proof quality items (pruflike).

To further aggravate the situation is an attempt to "improve" the safety of coins by mechanical or chemical means. In our opinion, only careful and professional handling of numismatic material will help to avoid trouble. Consequently, the aesthetic side of your hobby will be provided.

Like Phoenix, who has known the joy of rebirth, the restoration of coins gives a chance to resurrect the echoes of the former greatness of different countries and peoples. But once embodied in ringing gold, silver, bronze, copper and other metals, coins fade, age and rust over time.

And in order to return them to their presentation, cleaning and restoration is carried out. But do not rush to take radical measures, as inept actions can only do harm. In some cases, darkened silver, tarnished gold, patina of different shades - looks especially natural and expensive.

Restoration and cleaning of coins: the starting point is the degree of preservation

To navigate in the whirlpool of eternal values, the classification of states will help, according to which the restoration and cleaning of coins will receive the right direction.

Of course, from the first real ones that appeared in the 4th century BC. in Lydia, not much has survived. But even today, many other copies pass from hand to hand, representing the subjects of the eternal hunt of collectors.

With minimal damage and abrasions, practically uncirculated, coins can correspond to the highest degree of safety, indicated by the icons: UNC or AU.

Good preservation (XF, VF and F) can characterize exhibits that have been in circulation for a long time, but at the same time, have avoided significant damage. These coins have a contrasting pattern and the smallest relief elements are distinguishable, while scratches, notches and burrs are not deep, but for the most part there is no metallic sheen.

When only large details and the main contours of the relief are distinguishable, there are scratches and even notches, and the inscriptions and the date of minting are almost invisible, the condition is considered to be satisfactory. Icons are used for its marking: VG or G.

Cleaning and restoration of coins: the best ways to restore

An event such as coin cleaning and restoration requires the supervision of specialists who know how not to harm the product. Are you afraid to ruin the coin by chemical or mechanical action on the surface? D

To begin with, just wash off the dirt from it with warm soapy water and a soft brush or cloth. This will be sufficient for gold and some samples of silver. And in case of oxidation, you can use a solution of ammonia or gruel from moistened soda. But in any case, the coin cleaning procedure will be completed by washing in clean water and drying with a soft cloth.

For copper coins, in addition to soapy water, table vinegar will justify itself. And how long the object is in the solution (several minutes or hours) will tell its condition, size and type of plaque.

Extreme care will also be required when working with iron and zinc coins, since rust can only be removed from them with a knife or scalpel. True, there is a chance to use dilute hydrochloric acid and a brass wire brush, but the main thing here is not to harm the drawing.

But chasing from tin, lead and aluminum does not tolerate chemicals. To remove dirt in this case, it is better to use a glass brush and a cloth made of felt or cloth.

Coin cleaning: arguments for and against

Jewelery and pots definitely need cleaning, and cleaning coins does not always lead to increased value. The natural look and traces left by time give the exhibits a special historical and collectible value.

Be that as it may, only the voice of a specialist who owns the necessary devices and materials will be decisive. Inept restoration often leads to the exposure of mountain ash, erased drawings and shells, which does not add value in any way.

There are many ways to clean coins, but you should never use untested tools, but it is better to experiment on items that are not of particular value.

We will introduce you to safe methods of cleaning coins from an archaeological metal restorer with many years of experience in the Hermitage. An article about these methods of cleaning was posted in the book "The Past of Our Motherland in the Monuments of Numismatics". The author of the useful material is Olga Vasilyeva, an employee of the Hermitage. Let's move on to the most useful excerpts from the text.

coin clearing- one of the responsible types of restoration, it is important for their study, dating, identification and storage.

Ancient coins made of silver and copper alloys, found in hoards or other archaeological excavations, most often arrive at the restoration workshop heavily corroded, sometimes completely mineralized. Under the influence of water and salts, copper is destroyed in the soil with the formation of green carbonates and chlorides, red copper oxide and black oxide. Compounds of tin and lead are found in the corrosion layers on bronze coins. Silver-copper alloy coins are often coated with copper corrosion products. Sometimes silver under the influence of chloride salts turns into gray-violet chloride, horn silver. In air, copper alloys darken from oxidation, and silver - as a result of the formation of sulfide.

Restorers are always very careful about the restoration of numismatic monuments. In particular, they make the right choice of the reagent necessary for cleaning from corrosion, since a reagent that is successfully used for some coins may be unsuitable for others and will lead to their destruction or distortion of their appearance. It is desirable to achieve and preserve a noble patina, a kind of certificate of antiquity of objects.

So, when you start cleaning coins, you should first of all find out what metal they are made of, whether they have a metal core, to what extent it has been preserved, what salts the coins are covered with.

Cuprous chloride

It is important, for example, to determine the presence of copper chloride in corrosion crusts on copper coins, which in humid atmospheric conditions causes an active corrosion process - “bronze disease”. To detect copper chloride, a humidification chamber is used: a glass vessel is filled with water by about 1/7 of the volume; a perforated plate made of plastic, plexiglass or porcelain is placed above the water, on which coins with a corrosive layer are placed. The container is tightly closed with a lid. In this state, it is left for 1-3 days.

The action of the humidification chamber is to accelerate the processes occurring under the influence of air humidity, which helps to identify active corrosion centers and makes it possible to choose more successful cleaning methods. Even the presence of coins in the chamber contributes to the loosening of the surface layer of oxides, facilitating further cleaning operations. If there is copper chloride in the corrosion layer, then droplets of a colorless or slightly greenish liquid appear on the surface of the coins. Otherwise, the droplets do not come out: copper carbonate, nitrous oxide and copper oxide are stable in wet conditions (horn silver on silver coins is also stable). And if copper chloride is found, it must be removed from the deepest pores and very thoroughly.

zalipukhi

Often, during excavations, coins are found boiled, forming a shapeless mass. We do not recommend disconnecting such coins by heating them and lowering them into cold water. To avoid losses, such a lump should be placed in a 5-10% sodium hydroxide solution and heated to 30-50 ° C. After that, the coins can be separated from each other, determine the condition of each of them and start cleaning.

Cleaning methods

The main ways of clearing coins are mechanical, chemical and electrochemical. During restoration, a combination of the mechanical method with others is practiced.

Machining consists in removing surface layers: earth, sand and individual corrosion bumps. It is produced using various brushes, scalpels and dental burs of various sizes. But when used roughly, they can easily cause scratches that will distort the inscription, images, etc.

copper coins

The chemical method, combined with the mechanical method, cleans coins covered with a thick layer of corrosion products, but retaining a metal base, as well as coins made of gold and silver.

If copper coins are covered with salts consisting of copper carbonate (dark green), these layers should be removed with a 5-10% solution of citric acid. It slowly dissolves copper salts and oxides and does not dissolve metallic copper.

There are also copper coins covered with a yellowish-pale coating of lead carbonate. This suggests that there is a lot of lead in the alloy of the coins themselves, or they were lying in the ground with lead objects. To remove such plaque, a 10% solution of acetic acid should be used, which easily dissolves lead carbonate.

The restorer often has to deal with fully mineralized coins that are not always preserved. The success of the treatment depends to a large extent on which compounds have replaced the metal as a result of complex mineralization processes. First, the surface deposits should be carefully removed. If in this way it is possible to reveal one or another ornament, inscription, etc., then this should be limited. If mechanical processing did not open the coin, a 5% solution of caustic soda or ammonium carbonate is used.

Attention! Since the degree of preservation of coins is different, it is difficult to give recommendations regarding the time of their residence in one or another reagent. Therefore, periodically removing the coins from the solution, you should gradually remove the softened layers mechanically, thus contributing to the acceleration of the cleaning process.

silver coins

Cleaning of silver coins is carried out mainly in a chemical way. Such cleaning is reduced to the removal from the surface of oxides and salts of other metals, mainly copper compounds. Copper compounds on silver coins are recognized by their green color. To remove them, you need to put a coin in a glass vessel or in a porcelain cup and pour 5% sulfuric acid solution. To speed up the process, it is possible to carry out cleaning with heated solution, from time to time removing the coin, rinsing with water (preferably running water), then brushing off the mechanically softened salts with brushes. You can also use a 5-10% solution of formic acid, preferably heated to 50-70 ° - the hotter the solution, the stronger its effect.

The formations of violet-gray horn silver are exceptionally soft. Such coins often lack a metal core, and the possibility of their complete loss cannot be ruled out during cleaning. But if the crust of horn silver is not too thick, the coin can be immersed in a 5-10% ammonia solution. In these solutions, horn silver softens, after which it is carefully removed mechanically.

A brass brush is a restorer's tool.

For coins that have retained a metal core, but have very dense, hard, thick oxides, as well as fragile coins, the electrochemical reduction method can be applied. This method does not require special equipment. Zinc and aluminum are commonly used for electrochemical processes. Practice has shown that for cleaning coins it is best to use plates made of sheet zinc or aluminum, with holes punched into them (like a grater). Formic acid of 5-10% concentration is taken as an electrolyte. A zinc or aluminum plate is placed at the bottom of the glass vessel. Several coins are laid out on the grated surface of the plate, which are covered with the grated surface of another similar plate. After that, the vessel is filled with the prepared solution so that the coins with the plates are completely hidden.

Processing in this way should be carried out with particular care and caution, with frequent monitoring of the progress of the process. Mechanically removing the restored and softened corrosion products, the coin is examined through a magnifying glass to determine the degree of its purification.

Note that gold and new coins that have not been in the ground, but have only been in circulation for a long time, are cleaned easily and quickly. It is necessary to remove fatty substances from them with acetone, gasoline or alcohol and lower them into a 5-10% solution of citric or formic acid.

After cleaning

After cleaning the coins in one way or another, they should be thoroughly washed (digested) in several changes of boiling distilled water until the water reacts neutrally according to the universal indicator. After washing, the coins are dried in acetone, then in alcohol for 30-60 minutes. For this purpose, you can also use a thermostat (special drying cabinet), keeping coins in it for no more than two hours at a temperature not exceeding 100 ° C.

After conservation, it is necessary to store coins and medals not in heaps, but in separate cells of albums or in trays with compartments.

Additional information about the restoration of metal can be found in the books "Conservation and Restoration of Museum Collections" by M. V. Farmakovsky and "The Conservation of Antiquities and Works of Art" by H. D. Plenderlis.

Well, about more modern methods of cleaning coins with the help of effective means, read on "MDRegion" and look at our channel on YouTube.

What is a chemical engineer? This is a universal worker in the laboratory, he does everything - he washes chemical dishes, prepares solutions, calibrates instruments, conducts complex experiments, writes reports. I am a chemical engineer in a research lab with a great team.

According to the specifics of the work, the laboratory is engaged in research work in various fields: in ecology - it develops methods for treating wastewater, in agriculture - soil fertility analysis, in construction - it develops modification additives for concrete, in medicine - the analysis of drugs. When my friends hear what I do at work, I immediately start asking - to check their water, soil from the garden, etc. Since I am not always busy with work, I always do such work, for certain bonuses, with pleasure.
But one day my friend Lena turned to me, who had a coin that she inherited from her great-grandfather.

Over the long years of lying at the bottom of the box, the coin, already splattered with mud, completely turned black and began to corrode. A friend is not keen on collecting, but she really wanted to make money on a coin.

After going through antique shops, a friend found out that two coins of the same year of issue can have different values, due to the assignment of one of ten safety categories to them. Her coin did not have dents, cracks, it was only heavily oxidized, but because of this, it lost a lot of value. So the task was before me and my colleagues - to return the little thing to its original chic and brilliance.

Having received a coin, I arranged a consultation at work, read the relevant literature, calculated the concentrations of solutions, time, temperature. Together with a colleague, I assembled an installation from the required number of galvanic baths. We started. An hour later, I had in my hand a copper coin of Nicholas II with a face value of 1/2 kopeck, issued by the St. Petersburg Mint in 1984, currently worth $ 400.

And solemnly handing her friend her coin, listening to her words of gratitude, brushing off her notes of gratitude, I realized that you can really make good money on this. Lenka is not the only one who has such a house lying around, as many consider “trash”.

Inspired, I posted an ad on a local website with the headline "metal antiques restoration." The people responded, brought coins, glasses, spoons, forks. Not many, but there were customers, the guys and I enthusiastically approached each order, it was very interesting what would happen. It's nice to give new life to things that have long lost it.

At my own peril and risk, I decided to move on and advertised on the Internet on coin auction sites, treasure hunt forums. The work began to take on new momentum. It turns out that there are not so many people involved in restorations. Parcels began to arrive from other cities with ancient coins, daggers, icons, vases, candlesticks. The most unusual items for restoration were: a photo frame from 1900, a writing set from 1880, a purse from 1890, a mirror from 1920 and even a fireplace screen.

At first, it was very scary to hold an ancient thing in your hands, lower it into a solution of boiling acid or alkali, having only one attempt to make “candy” out of it. Things found by archaeologists in treasures are very strongly corroded, and sometimes completely mineralized. Coins are sometimes found "boiled" - stuck together, due to the action of salts and dirt into a shapeless mass.

In the work of a restorer, the main thing is not to make a mistake in choosing a reagent and cleaning technology, since what was good for one thing may be completely unsuitable for another. As a sapper, there is no room for error. But everything comes with experience. Each time, the work began to be done more and more confidently.
After cleaning and polishing, coins and other items, at the request of the customer, are preserved in a layer of paraffin or synthetic resins.

Here is such an interesting and very profitable left earnings available for chemical engineers. Thanks to the teachers who taught me everything that I can do.

Ideas for Business from the section:

Cleaning ancient coins.
(Ed.: "The past of our Motherland in the monuments of numismatics." Leningrad, 1977).

The purpose of this report is to acquaint interested readers with the simplest and safest methods of cleaning coins, which the author can recommend based on his many years of experience in the restoration of archaeological metal in the State Hermitage.

Clearing coins is one of the responsible types of restoration, it is important for their study, dating, identification and storage.
Ancient coins made of silver and copper alloys, found in hoards or other archaeological excavations, most often come to the restoration workshop heavily corroded, and sometimes completely mineralized. Under the influence of water and salts, copper is destroyed in the soil with the formation of green carbonates and chlorides, red copper oxide and black oxide. Compounds of tin and lead are found in the corrosion layers on bronze coins. Silver-copper alloy coins are often coated with copper corrosion products. Sometimes silver under the action of chloride salts turns into gray-violet chloride - horn silver. In air, copper alloys darken from oxidation, and silver - as a result of the formation of sulfide.
The restorer must be very careful about the restoration of numismatic monuments. In particular, it is necessary to make the right choice of the reagent necessary for cleaning from corrosion, since a reagent that is successfully used for some coins may be unsuitable for others, i.e., it will lead to their destruction or to serious distortions of their appearance. It is desirable to achieve and preserve the "noble patina" - a kind of certificate of antiquity of objects.
When starting to clean coins, you should find out: what metal they are made of, whether they have a metal core, to what extent it has been preserved, what salts the coins are covered with.
It is important, for example, to determine the presence of copper chloride in corrosion crusts on copper coins, which in humid atmospheric conditions causes an active corrosion process - "bronze disease".
To detect copper chloride, a humidification chamber of a simple device is used: a glass vessel is filled with water by about 1/3 of the volume; a perforated (perforated) plate made of plastic, plexiglass or porcelain is placed above the water, on which coins with a corrosive layer are placed. The container is tightly closed with a lid. In this state, it is left for 1-3 days.
The action of the humidification chamber is to accelerate the processes occurring under the influence of air humidity, which helps to identify active corrosion centers and makes it possible to choose more successful cleaning methods.
In addition, the presence of coins in the chamber contributes to the loosening of the surface layer of oxides, facilitating further cleaning operations. If there is copper chloride in the corrosion layer, then droplets of liquid, colorless or slightly greenish, will necessarily appear on the surface of the coins. Otherwise, the droplets do not come out: copper carbonate, nitrous oxide and copper oxide are stable in humid conditions (note that horn silver on silver coins is also stable). If copper chloride is found, it must be removed from the deepest pores and very thoroughly.
Often, in archaeological excavations, coins are found “boiled”, i.e., forming a shapeless mass due to the oxides connecting them. We do not recommend separating such coins by heating them and lowering them into cold water. sodium hydroxide solution and heat up to 30-50 °. After that, the coins can be separated from each other, determine the condition of each of them and start cleaning.
The main ways of clearing coins are mechanical, chemical and electrochemical. During restoration, a combination of the mechanical method with others is most often practiced.
Machining consists in removing surface layers: earth, sand and individual corrosion bumps. It is produced using various brushes (bristle, brass and glass fiber), scalpels and dental burs of various sizes. However, these tools must be used with great care. With inept and rough use, they are easy to scratch, which to some extent distort the inscription, images, etc. Chemically, in combination with a mechanical method, coins are cleaned, covered with a thick layer of corrosion products, but retaining a metal base, as well as coins from gold and silver.
To remove a cherry-red coating of cuprous oxide from copper coins, you should lower the coins into a 5-15% ammonia solution, but so that they are completely immersed in the solution, because in contact with air, the effect of ammonia on the metal is destructive. Instead of ammonia, you can successfully use a 5-10% solution of ammonium carbonate, which is less aggressive towards copper and bronze. If copper coins are covered with salts consisting of copper carbonate (dark green), these deposits should be removed with a 5-10% citric acid solution. It slowly dissolves copper salts and oxides and does not dissolve metallic copper.
There are also copper coins covered with a yellowish-pale coating of lead carbonate. This suggests that either there is a lot of lead in the alloy of the coins themselves, or they were lying in the ground with lead objects. To remove such plaque, a 10% solution of acetic acid should be used, which easily dissolves lead carbonate.
Sodium hexametaphosphate (G.M.F.N.) can serve as a “softener” for corrosion layers on copper coins. It is a vitreous, highly soluble salt. It must be dissolved with continuous stirring, since the vitreous mass sticks to the bottom of the vessel. M.F.N. is used in the form of a 5-20% solution.In a cold state, it acts slowly.To speed up the process, it is necessary to heat the solution to 60-80 °.
G.M.F.N. absolutely safe for metal and due to the slow action allows you to easily follow the progress of cleaning and use mechanical processing in a timely manner.
The restorer often has to deal with coins that are completely mineralized, which are not always possible not only to open, but also to save. The success of the treatment depends to a large extent on which copper compounds have replaced the metal as a result of complex mineralization processes. First, you should carefully, without physical stress, remove surface layers. If in this way it is possible to reveal one or another ornament, inscription, etc., then this should be limited. If mechanical processing has not "opened" the coin, a 5% solution of caustic soda or ammonium carbonate is used.
Taking into account that the degree of preservation of coins submitted for restoration is different, it is difficult to give definite recommendations regarding the time of their residence in one or another reagent. Therefore, periodically removing the coins from the solution, one should gradually remove the softened layers mechanically, thus contributing to the acceleration of the clearing process.
Cleaning of silver coins is carried out mainly in a chemical way. Such cleaning is reduced to the removal from the surface of oxides and salts of other metals, mainly copper compounds. Copper compounds on silver coins are recognized by their green color. To remove them, you need to put the coin in a glass vessel or in a porcelain evaporating cup and pour 5% sulfuric acid solution. To speed up the process, it is possible to carry out cleaning with heated solution, from time to time removing the coin, rinsing with water (preferably running water), then cleaning the mechanically softened salts with brushes - bristle or glass fiber. With repeated operations of this kind, the layers gradually decrease and completely disappear. You can also use a 5-10% solution of formic acid (preferably heated to 50-70 °). It softens well and removes oxides and carbonic compounds of copper on silver. The hotter the solution, the stronger its effect. The formations of violet-gray horn silver are exceptionally soft. Such coins often lack a metal core, and the possibility of their complete loss cannot be ruled out during cleaning. But if the crust of horn silver is not too thick, the coin can be immersed in a 5-10% solution of ammonia or ammonium chloride. In these solutions, horn silver softens, after which it is carefully removed mechanically.
For coins that have retained a metal core, but have very dense, hard, "thick" oxides, as well as fragile coins, the electrochemical reduction method can be applied. This method does not require special equipment. Zinc and aluminum are usually used for electrochemical processes. Practice has shown that for cleaning coins, it is best to use plates made of sheet zinc or aluminum, with holes punched in them (like a grater).Caustic soda or formic acid of 5-10% concentration is taken as an electrolyte.At the bottom of a glass vessel (it is clearly visible recovery process), the aforementioned zinc or aluminum plate is placed. Several coins are laid out one to the other on the “worn” surface of the plate, which are covered with the “worn” surface of another similar plate. After that, the vessel is filled with the prepared solution so that the coins with the plates are completely hidden.
Processing in this way should be carried out with particular care and caution, with frequent monitoring of the progress of the process. Mechanically removing the restored and softened corrosion products, they examine the coin through a magnifying glass to determine the degree of its clearing. After inspection, if necessary for a clearer identification of the image, it is again subjected to electrochemical processing.
Note that gold and "new" coins that have not been in the ground, but have only been in circulation for a long time, are cleaned easily and quickly. Fatty substances must be removed from them with acetone, gasoline or alcohol and lowered into a 5-10% sulfuric solution. , citric or formic acid.
After cleaning the coins in one way or another, they should be thoroughly washed (“digested”) in several changes of boiling distilled water until the water is neutral according to the universal indicator and soluble chlorides are completely removed: the cooled sample of the last wash water should not become cloudy from the introduction of a drop of 1.7 % solution of silver nitrate.
After washing, the coins are dried in acetone, then in alcohol for 30-60 minutes. For this purpose, you can also use a thermostat (special drying cabinet), keeping coins in it for no more than two hours at a temperature not exceeding 100 ° C.
Copper coins that showed signs of bronze disease are again placed in the humidification chamber after cleaning. If drops of copper chloride appear in some places, these pockets are carefully cleaned mechanically, and the coins are “boiled” again.
If copper coins have an unpleasant sheen after cleaning, a light to dark brown patina can be artificially created. To do this, you need to take 50 g of copper sulfate and 5 g of potassium permanganate per liter of distilled water. In the prepared solution, heated to 70-80 °, lower the coins and hold until the desired shade is obtained.
After drying, the coins must be preserved with a protective coating - paraffin or synthetic resins. For this, 5% solutions of polybutyl methacrylate in acetone, toluene or xylene and polyvinyl butyral in alcohol or a mixture of alcohol and benzene (1: 1) can be recommended.
After conservation, it is necessary to store the coins not in “heaps”, but in separate boxes or trays with compartments. In this form, they will not touch and better retain their protective coating. In addition, when examining restored coins, it will be easier to identify those on which corrosion has reappeared.
Additional information about the restoration of metal can be found in the books "Conservation and restoration of museum collections" by M. V. Farmakovsky (Moscow, 1947) and Kh. , No. 10-11).

Coin cleaning, option 2.
Coin cleaning is the process of removing a layer of dirt and more or less significant traces of oxidation from the surface of a coin. The easiest way to remove dirt. It can be removed by washing in warm soapy water or using a soft brush. Moreover, this method is suitable for absolutely all monetary metals.
It is more difficult with oxidation. Because in this case it is necessary to take into account the nature of the monetary metal. If it is gold, then washing in warm soapy water is sufficient. If it is silver, then it is desirable to know the sample of the coin alloy.
Silver not lower than the 625th test is cleaned with a special tool - a silvertauschbader. An effective remedy is also a solution of ammonia, as well as an acidic fixer used by amateur photographers.
Base silver can be cleaned by immersing it in lemon juice for several hours. But in all cases with the cleaning of silver, the simplest and most affordable means is to wipe the coin with a slurry of moistened sodium bicarbonate, in other words, baking soda.
Silver coins are immersed in the solution in such a way that they do not lie tightly on the bottom or on top of each other. They need to be turned over from time to time. After complete removal of plaque, the coins should be wiped with a soft cloth.
All copper coins are washed in warm soapy water. The easiest way to clean copper coins is to soak them in a 5-10% solution of acetic acid. Simple table vinegar will do the same. Depending on the condition, size and type of plaque, coins should be in solution from several minutes to several hours or even longer. They also need to be stacked, turned over and wiped, as is the case with silver coins.
To apply this cleaning method, you must first figure out what kind of oxide layer is on the coin. The most detrimental thing for a coin is the so-called. "copper" (green copper). This is a poisonous oxide layer based on copper acetate, which appears under the influence of acetic acid vapor, which interacts with atmospheric oxygen.
The formation of verdigris is also possible on silver coins with a significant copper content. In this case, the so-called. "flowers" that are difficult to remove. In general, it is better to entrust the cleaning of copper coins to a specialist.
A completely different matter is patina, a layer of oxides formed on the surface of a metal under the influence of oxygen, carbon, acids and salts. It does not spoil the coin, but rather preserves it. Patina is considered beautiful and valuable, and its presence is often a sign of authenticity. The patina, as it were, preserves the coin, so it is not recommended to remove it.
Iron and zinc coins require a particularly careful approach. To clean these coins, it is recommended to wash them in dilute hydrochloric acid, followed by cleaning them with a brass wire brush.
With these types of coins, it is recommended to very carefully, with the tip of a knife or scalpel, remove rust and whitish deposits. At the next stage of cleaning these coins, vigorous rubbing against a piece of cloth or felt, dense fabric helps well. If you resort to treatment with a solution of hydrochloric acid, then you need to be very careful with the degree of its concentration, because. if the concentration is excessive, the drawing on the coin can simply "burn out". After treating the coins with a salt solution, they should be washed in warm soapy water and wiped dry with a soft cloth.
Lead, tin or aluminum coinage is not recommended to be cleaned with chemicals. Slight traces of dirt can be removed with a so-called glass brush. Friction on felt or cloth helps well. After cleaning coins of any metal, copious rinsing in warm and cold water is necessary to prevent re-damage to the surface.

Electrolysis.
Warning: While electrolysis is a popular form cleaning ancient metal objects, especially coins, there is a certain danger inherent in the use of any electrical device. The creation and use of such a device should be carried out in a well-lit and ventilated area using safety equipment such as goggles and rubber gloves. Even if the risk of death from electric shock is extremely low, you should never relax while using any electrical device.
Electrolysis is a quick way to clean coins. What takes months with olive oil can be done in minutes (and even seconds!) with electrolysis. Of course, this increases the risk of destroying your coin. Even with great care, you can get an unsatisfactory result, although initially a dirty coin showed great promise. Since electrolysis strips the coin of its patina, you are playing a game of chance, the outcome of which depends on how good the core of the coin is. Sometimes it happens that the coin consists entirely of one patina.
The first thing you need is an old 6 to 12 volt power supply. Higher voltage increases the risk of electrocution with little improvement in cleaning efficiency. Cut off the plug on the end of the power supply wire. Divide the end of the wire into two parts and strip the ends of the insulation. Twist the copper strands and, if possible, connect them to metal clamps. For example, for $3 you can buy a dozen of Radio Shack's copper-plated micro alligator clips.

Put it all aside and take a not very deep plastic bowl. Fill it with water to the depth necessary to clean the coin you have chosen, and dissolve the table salt in it. You shouldn't take a lot of salt, just a couple of spoons or so.
Connect the power supply to the mains, keeping the two clamps away from each other. If they touch, a short circuit will occur and the power supply will fail. Dip the clamps into the solution and notice which will release gas and hiss. You must connect this clip to the coin. Connect the other clip to a metal object. It can be something small, like a key or a spoon. Don't use copper or brass for this, as they don't work very well. You now have an electrolysis kit.
Dip both clips into the solution and your coin should begin to sizzle and bubble. Depending on how thick the layer of dirt and oxides is on your coin, the cleaning process should last from half a minute to several minutes. The coin should bubble vigorously. If the gas release is small, then this is also not bad, just the process will go more slowly. The rate of electrolysis can be increased by adding more salt to the solution, or by bringing the clamps closer together without actually touching them.
Remove the coin from the solution and clean it with a toothbrush with a drop of liquid soap. If you've kept the coin in the solution long enough, the dirt should start to fall off, but you may need to repeat the electrolysis process again. Very stubborn impurities may not succumb to electrolysis at all and must then be removed with a knife or other mechanical tool.
After a while, you will notice that the solution in the bowl will become dirty. This does not come primarily from the coin, but rather from the metal anode that dissolves into the solution. You should replace the solution as often as the anode as it wears out.

The easiest and safest way to clean coins.
Clearing coins is one of the most important types of restoration, to study their dating, determine the country in which they were minted and their subsequent storage.
Ancient coins made of silver and copper alloys, found in hoards or during archaeological excavations, most often come to the restoration workshop heavily corroded, and sometimes completely mineralized.
Under the influence of water and salts, copper is destroyed in the soil with the formation of green carbonates and chlorides, red copper oxide and black oxide. Compounds of tin and lead are found in the corrosion layers on bronze coins.
Silver-copper alloy coins are often coated with copper corrosion products. Sometimes silver under the action of chloride salts turns into gray-violet chloride - horn silver. In air, copper alloys darken from oxidation, and silver - as a result of the formation of sulfide.
The most common problem is copper cleaning. Under the influence of a humid atmosphere, salt and sulphate compounds in the air, as well as in the ground, copper is destroyed with the formation of chlorides, green carbonates, black oxide and red oxide of copper, copper alloys darken from oxidation by atmospheric oxygen.
It is necessary to be very careful when cleaning and restoring numismatic monuments. First of all, a properly selected chemical reagent necessary for removing corrosion will give you a guarantee for the entire further restoration process. However, a well-chosen reagent in some cases may be completely unsuitable for other things and may lead to their destruction or serious distortion of their appearance.
The second task is to identify what metal the found coins are made of, and to what extent the corrosion process has affected the metal itself, that is, how deep the decay process has gone.
Preliminary preparation for restoration requires the involvement of the work of chemical and physical laboratories to clarify the first two tasks, which, of course, is not always possible. Here are the most simple tips available to almost everyone in our time.
Often in archaeological excavations, coins are found "boiled", that is, they form a shapeless mass due to the oxides connecting them. We do not recommend disconnecting such coins by heating them and lowering them into cold water. In order to avoid losses, such a "lump" should be placed in a 5-10% sodium hydroxide solution and heated to 30-50 °. After that, the coins can be separated from each other, determine the condition of each of them and start cleaning.
The main ways of clearing coins are: mechanical, chemical and electrochemical. During restoration, a combination of the mechanical method with others is most often practiced.
Machining is done using various brushes (bristle, brass or glass fiber), ordinary needles (sewing and medical), scalpels and dental instruments. They must be used with extraordinary care and great manual dexterity. With inept and rough use of this method, you can easily cause scratches that distort inscriptions, images, etc., or you can simply break the thing.
Copper coins must go through a chemical process before being machined. For this, it is best to use a 5% sodium hydroxide solution or a 5-10% ammonium carbonate solution, which dissolve and soften copper salts and oxides and do not damage metallic copper. To do this, the coins are completely immersed in the solution and kept in it for at least 24-48 hours. Then the coins must be washed and mechanically processed, preferably with a brass brush. Depending on the extent to which it was possible to remove the corrosion products, this process can be done again.
Taking into account that the degree of preservation of coins is different, it is difficult to give definite recommendations regarding the time of their residence in a particular reagent. Therefore, periodically removing the coins from the solution, it is necessary to gradually remove the softened layers mechanically. After we see that the surface of the coin has got rid of the cherry-red coating of cuprous oxide, the yellowish-pale coating of lead carbonate or the bright green of copper chloride, we must proceed to the next stage, the so-called "digestion". Coins must be thoroughly rinsed in several changes of boiling (preferably distilled) water until the water is neutral. In most cases it is better to boil them in several waters.
After washing, it is necessary to dry the coins by placing them in acetone, and then in alcohol for at least 30-60 minutes. You can also use a special cabinet (thermostat) for this purpose, keeping coins in it for no more than two hours, at a temperature not exceeding 100 ° C. I would especially like to pay attention to copper coins that had the green of copper chloride. After cleaning, they must be placed in a humidification chamber. If points of copper chloride appear in some places, these centers are carefully cleaned mechanically (with needles, dental instruments) and the coins are "boiled" again.
After the final drying on the coins, it is better to create a protective layer. To do this, the coins are covered either with a special varnish, or with paraffin or synthetic resins. Cleaning of silver coins is carried out mainly in a chemical way. To remove silver oxides, it is best to use a 5-10% solution of formic acid, which softens well and removes not only oxides, but also copper carbonates on silver. Silver coins are placed in a solution of formic acid, in glassware, and the process of cleaning them will take place before our eyes. To speed up the process, it is possible to carry out cleaning with heated solution, from time to time, removing the coin, rinsing it with running water, then cleaning the mechanically softened salts with brushes - bristle or fiberglass. After cleaning silver coins, a washing and drying method similar to the method with copper coins should be applied.
The simplest cleaning method is applied to gold and platinum coins, which is mainly preventive cleaning, i.e. to remove fatty substances and dirt that have formed as a result of a long stay in the ground. Fatty substances are removed with the help of medical cotton wool,
moistened with acetone or alcohol.
After drying, the coins must be preserved, covered with a protective layer - paraffin or synthetic resins. To do this, we can recommend 5% solutions of polybutyl methacrylate in acetone, toluene or xylene and polyvinyl butyral in alcohol or a mixture of alcohol and benzene in a ratio of 1:1.
After conservation, it is necessary to store coins in separate boxes or trays with compartments. In this form, they will not touch and better retain the protective coating. In addition, when examining restored coins, it will be easier to identify those on which centers of corrosion have reappeared.