Gold as one of the elements of the platinum group belongs to the category of noble metals. These elements are highly resistant to corrosion and inert to other materials, both metallic and nonmetallic.
Why gold can oxidize and change color. Rust as a product of oxidation
One of the main properties of the gold metal, along with its rare occurrence in both rock and nuggetsis weak susceptibility to oxidative processes. Because of this, it can be preserved in the Earth's strata as individual small objects, grains or placers, which do not react with other elements. They have an even luster, are characterized by a yellow color various shades.
Gold found in the natural environment or smelted from ores and refined, that is, cleaned of impurities, is used in the manufacture of a wide range of products. It is used in the production of industrial equipment, electronics, aerospace and nuclear industry.
An essential part of the mmetal is used to replenish countries' gold reserves in the form of smelted ingots, and gold coins are produced. The traditional use of the gold material is in the jewelry business and production of jewelry.
Jewelry is not made of pure 100% gold or even 24-carat gold.
The latter corresponds to 999 proofIt has less than 0.1 % of impurities. It can be used to make coins, usually collector's coins, gift coins, jubilee coins. For jewelry this material is too soft and can be scratched even with a fingernail.
To give strength and malleability to products, create gold alloys with other metals, conduct alloying by adding ligatures. In metallurgy, a ligature refers to the production of an alloy from two or more components by introducing refractory components into the liquid base metal. The additional elements are usually other precious metals, but base metals can be added. A variation of the elements creates alloys with the desired characteristics.
Dilute the gold
- and other metals.
The addition of additional elements affects the gold grade. The most popular gold qualities for jewelry making in our country are 585, corresponding to 14 carats, and 750, corresponding to 18 carats. Gold grade determines not only its appearance but also the quality of the metal, i.e. its strength, resistance to environmental influences, hardness and durability.
Sometimes on the gold articles Foreign stains appear, similar to rust or patina. This begs the question, is rust possible on gold? When metal rusts, it means that its particles have reacted with oxygen in the atmosphere and water. This is not characteristic of gold under normal conditions.
In order for the oxidative process to begin, it must be heated to very high temperatures or placed in solutions of certain substances.
For example, compounds with fluorine (F) occur when temperatures reach about 300 degrees. The reaction with chlorine (Cl) occurs at room temperature in a solution of "aqua regia", a mixture of nitric and hydrochloric acids.
But such extreme options are not available in the usual environment. Gold's inert, neutral character suggests that it cannot rust. Stains on gold items owe their appearance to various ligatures, as well as to some specific external conditions.
An example of this anomaly is the Georgy Pobedonosets investment coins issued by the Central Bank of Russia.
The loud scandal of the rusty St. George the Victorious. Several popular explanations for corrosion
Investors who bought gold banknotes to preserve their capital began to notice changes in the coins with the image of St. George striking the serpent. They were expressed in the fact that after several years of storage on them came through reddish, brown spots and stripes. The fuss was made by the famous Russian entrepreneur German Sterligov back in 2010. He demonstrated the "defective" coins on the TV channel "Dozhd".
The examination showed that the banknotes were made of 24-carat gold at the St. Petersburg Mint - SPMD.
The banks issuing them began to offer their own explanations for the anomaly.
- SMP Bank called the local color change "patina.
This is an oxide-carbonate film that forms on decorative items over time, among metals its appearance is characteristic of copper and its alloys, such as bronze and others. If coin gold was low-grade, with the addition of a large percentage of impurities, then the explanation could be considered reasonable.
But the 999th hallmark excludes such additives and, consequently, patination of the precious metal.
- Ak Bars Bank offered a hypothesis about the contact of gold with the hands of the owners, which resulted in the formation of oxides. They touched objects around them, brushed their teeth with fluoride paste, touched mercury-containing batteries - and lo and behold, rusty gold. Greasy fingerprints led to oxidation. The same applies to abnormal storage conditions. This explanation could be believed if centuries of history and science did not disprove it.
Gold is the most inert of all metals.
For an oxidation reaction to occur, you need to dip it into hot selenic acid, an aqueous solution of cyanide, royal vodka or heat the medium to 200-300 degrees. You can, of course, dissolve it in mercury to form amalgam, a readily fusible compound. Amalgamation is one of the ways to extract metals from ores. It is rather difficult to assume that the owners of the coins carried out one of such procedures.
Hence, a more rational explanation of the phenomenon relates to the effects of external factors, such as production conditions, on the coins.
- This version is outlined by Rus-Bank: the reason, most likely, in the surface defect of the stamp, which forms the obverse and reverse of the banknotes. It is made of steel, that is, iron material, on which the film of gold is superimposed. This surface is in contact with the stamped product. If the layer is damaged, very small particles of iron get on the surface, hence the possibility of oxidation in the air. A visual effect of corrosion of the gold is created.
- Another version is the ingress of elements of iron in the process of rolling blanks for the manufacture of coins. In this case, its particles penetrate the workpiece. The smallest particle creates a halo of rust, spreading to neighboring layers of metal.
- Another version of the explanation appeared when the SPMD was examined.
Gold and silver coins were minted on the same machines. Chemical analysis showed that micro-particles of silver could fall on the gold workpieces, forming on them stains of the binary compound silver sulfide Ag2S. The hydrogen sulfide salt in the form of a film gives the silver a pinkish tone. This is just one of the shades that show up on the coins.
What to do and what not to do in case of rust on gold
If you find rust-like stains on your gold, do not rush to wash or scrub them off, as you could damage the piece or coin. It is better to turn to a jeweler who will professionally carry out restoration of the problem areas. Bankers consider the possibility of such defects to be a minor problem. Banks will buy back such coins at a small discount.
The high inertness of gold does not mean that there can't be contaminants and problems on it.
- For example, if iodine gets on the surface of the piece, it will destroy the outer layer, creating a grayish coloration. This is dangerous when the jewelry is coated with the thinnest protective layer of rhodium or ruthenium.
- Caution will not hurt when using household chemicals, cosmetics, perfumes and medicines.
- The skin and sweating habits of an individual can lead to changes in colors of precious metals.
All these variants are the most noticeable if the jewelry is of a low grade. All of these variations are most noticeable when the jewelry is of a low grade. 585 proof) give a greenish patina-like hue.
Gold-plated or rhodium-plated jewelry is prone to abrasion of the outer layer, from under which the original material emerges. It may appear yellow, reddish, gray, or another color.
Some change in the appearance of the jewelry will require its owner or mistress to tidy it up. There are many methods of cleaning, polishing, among which stand out the home ones using household remedies.
Question and answer on changing the color of gold
Color changes, loss of gloss, fraying, streaks and stains are unpleasant phenomena that you should take a close look at.
Can a new product lose its luster?
What causes white gold to turn yellow?
Causes of an oxidized neck chain?
Why is there blackness under the wedding ring on my finger?
Another reason for possible blackening is the use of special mastics, polishing pastes that give the product a shiny and dignified appearance. When they move to the leather, they leave dark streaks on it.
The gold doesn't change color, but the ring turns green?
Is it possible to prevent the oxidation of gold jewelry?
They are moistened with solutions of vinegar, soda, special compositions.
Some people use beer and Coca-Cola to clean and shine.
Does gold rust in water?
Does gold oxidize underground?
Does gold oxidize in air?
Does gold oxidize on the human body?
Does gold oxidize in the mouth?
Does gold oxidize in seawater?
Does gold oxidize in my ears?
Does iodine oxidize gold?
The precious metal reacts with halogens, which include iodine: it darkens at the application site. AuI - gold iodide - is formed. Over time, the stain disappears, as the binary compound is reduced to gold rather quickly. To avoid waiting, you can clean gold jewelry with hyposulfite from the drugstore.
Does gold rust or oxidize?
Pure gold is practically immune to oxidation under normal conditions. Only the creation of special regimes - chemical and temperature - causes such processes.
Top 3 ways to clean gold with your own hands
It is possible to clean jewelry made of noble metal at home. All you need to do is follow a few rules.
10% ammonia solution is a reliable, proven means for cleaning gold jewelry. Fill a glass or porcelain container with 200 ml of warm water, add 1 tbsp. washing powder or liquid soap and 1 tbsp. ammonia alcohol. Keep jewelry in the solution for about two hours, rinse under running water. Gently wipe with a soft cloth.
Boiling with dishwashing detergent
More soiled items are boiled in a solution of dishwashing detergent, placed on a soft cloth at the bottom of the container.
The treatment time is 7-10 minutes, then you need to remove them, rinse them, dry them with a soft towel or cloth.
Soaking in solution: liquid soap + ammonia + peroxide
A home remedy consisting of ammonia, hydrogen peroxide and soap in a glass of water. Each mixture is 1 teaspoon each.
A 10-minute soaking in the solution gives good results. After that, the product is washed and dried.
Video: banks' rusty gold
Peculiarities of cleaning gold with stones
Gold jewelry with stones requires special attention. Pearl, turquoise and coral inlays are not resistant to ammonia.
Diamonds feel differently - they look transparent and sparkling as a result of the procedure.
General rules for products with stones:
- Boiling is prohibited.
- The use of baking soda and vinegar should be avoided.
- Forget about brushes and sponges using powders.
Stones, like precious metals, can be wiped with soft cloths.
If severe oxidation occurs, it is advisable to contact a professional jeweler.
Express method of ring cleaning
A quick method of cleaning jewelry is good for daily care of it. It boils down to polishing with a soft cloth such as fleece, flannel or others. If you do it constantly, you can keep the shine and elegant appearance of rings, bracelets, chains and earrings for a long time.
Effective tools for cleaning jewelry at home
Different manufacturers offer a variety of jewelry cleaning products.
- devices with ultrasonic effect;
- effervescent soluble tablets;
- pastes and impregnations for cleaning;
- Wet wipes soaked in the right substance.
In all cases, you should carefully read the instructions for use. They may not be suitable for all types of jewelry.
Handy tools in the kitchen for cleaning gold
Any housewife will have simple everyday remedies for cleaning the noble metal in her kitchen.
Connoisseurs recommend the use of solutions:
- The sodium hydrogen carbonate, NaHCO3, is an acidic sodium salt of carbonic acid;
- salts - sodium chloride, NaCl;
- ammonia hydroxide, NH4OH.
The especially "advanced" ones advocate Coca-Cola and beer as cleansing mixtures.
Recommendations for choosing gold jewelry for long-term wear
Products made from different qualities of gold, with different techniques, require an appropriate approach. 18-karat gold 750 samples less fastidious to wear. For those who adhere to an active lifestyle, are engaged in sports and constantly wear decorationsIt's a good idea to choose such high-strength alloys.
The fewer different additives in the ligature, the better it wears and requires less maintenance.
Specific types of gold are whiteThe use of rhodium-plated or complex alloys, as well as non-ferrous precious metals, requires more care and constant maintenance. In addition, the coating must be renewed periodically.
Gold Care Tips
Gold jewelry is not difficult to care for, but it requires attention and care.
- Store in the special soft case.
- Take it off at night and before applying cosmetics.
- Periodically wipe and polish the surface of the jewelry. Use a soft, suede, fleece or velvet cloth.
- If necessary, clean and freshen your jewelry: treat it at home with improvised compounds or with specialized devices, pastes or impregnated cloths.
- Contact a jeweler to renew the plating and cleaning
Observance of simple rules will allow products made of precious metal to serve long, not to tarnish, to keep a decent look.