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Gold is a noble metal with aesthetic appeal and many valuable properties. Since in its pure form it has high cost, optimal solution involves applying a thin layer of gold to the surface of the product. There are different gilding techniques - their choice depends on the size of the object and the goals pursued.

Fields of application of gilding

Gilding is used in many areas of our lives - it is performed for protective, decorative, protective and decorative purposes. In particular, plating with 18 and 24 carat gold allows you to give a status look to jewelry made from silver or metal alloys, and also helps restore the beauty of gold items that have lost their original appeal.

Gilding of decor and household items improves the interior of apartments and houses - door handles, forks and spoons, taps, picture frames, metal parts of lamps, etc. are subjected to the procedure.

There is an increasing interest in gilding moldings, chrome inserts, car grilles, handles, and key rings. Plating discs with 24 carat gold, 18Kt/750, 14Kt/585 is practiced.

Plating with white, pink, green gold is used in the case of musical instruments, awards, sports accessories. The gilding of engravings, cigarette cases, lighters, flasks, weapon parts, etc. deserves special attention.

The thinnest layer of gold is sprayed onto car, window and stained glass glass to control heat transfer in winter and summer. Gilding is used in dentistry. It is widely used in microelectronics.

The technology involves the following main steps:

• choosing a gilding method and preparing everything necessary for its implementation;
• degreasing and surface etching;
• coating;
• finishing treatment.

In addition to sputtering the noble metal in its pure form (24 carats, 999 standard), plating with yellow, white, pink, red and green gold is practiced. The alloying additives used are cobalt, rhodium, copper, and silver (nickel). Instead of 24-karat metal, it is plated with gold of 18, 14, 12, 10, 9, 8 carats - the number means the weight units of pure gold in 24 parts of the alloy.

Technology of coating objects with gold leaf

Gold coating of plastic, wood, metal and other materials is carried out using the thinnest sheets - the thickness of gold leaf (cladding) is 0.13-0.67 microns. In the old days, gold leaf was made by hand, today special equipment is used. Depending on the thickness of the sheet, free and transfer (on silk paper) gold leaf is distinguished. It is very difficult to work with the first one - the slightest breath interferes with the process. The finished material is stored in little books - each of the 60 sheets is covered with paper. Applying gold leaf is a painstaking process. The technology is based on the ability of gold rolled out from a sheet to be attracted to the surface on molecular level. There are two techniques for gilding with gold leaf: glue (for polyment) and oil (for Mordan varnish). In the first case, a glossy surface is obtained, and in the second, a matte surface. The adhesive method is used when carrying out interior work.

Amalgam gilding

The amalgam (fire) gilding method is another ancient method of applying precious metal. It has a high degree of durability, but the process itself is extremely toxic and is not used today. The essence of the method is the molecular penetration of a precious metal dissolved in mercury into the base (during the firing process, the mercury evaporates, but the gold remains). An example of such work is the dome of St. Isaac's Cathedral in St. Petersburg.

Electroplating

The galvanic gilding process is the most commonly used process today. It is applicable when processing conductive products is carried out. The electrolyte becomes a solution of gold salts. A part is immersed in it - when a current passes, positively charged particles released from metal salts settle on the surface of the product and form an even layer of gold.

An even better result can be obtained using the selective method of electrochemical gilding. The use of this technique makes it possible to increase the rate of metal deposition on the product tens of times. The wear resistance and hardness of gold coating increases by more than 3 times. Gold penetration occurs at the molecular level. Electroplating methods are used in gilding souvenirs, jewelry, dentures, etc.

Immersion gilding technique

This type of gilding does not involve the application of external current. When a part is immersed in a solution of a less electronegative metal, the process of immersion deposition occurs. Once the contact exchange ends, it ends. The technology includes several stages - work begins with acidic surface cleaning and micro-etching, and ends with chemical deposition of a nickel layer and subsequent application of immersion gold. The technology finds application in production printed circuit boards, terminals of the element base, housings, microcircuits and other products that require ultrasonic welding or soldering.

Methods of chemical gilding

At home, gilding decor, covering spoons, decorative flowers and other metal objects with gold is carried out by rubbing their surface with gold chloride paste or immersing them in a solution with zinc contact. In the first case, gold is dissolved in a mixture of nitric and hydrochloric acids (1:3). The ratio of gold and solution is 1g/10 ml. The liquid is evaporated, observing safety precautions. The resulting gold chloride is combined with melted (extracted) chalk, cream of tartar and blood salt. After applying the paste with a brush, the object is left for a certain time. It is then washed and polished. By mixing gold chloride with ether, patterns and inscriptions are made.

To prepare a solution for gilding from gold chloride, distilled water (its temperature should be about 50-60 degrees), potash and salt are combined with it. A degreased, acid-etched and water-washed object is immersed in the solution and touched with a zinc stick. Once the gold deposition process is complete, the item is washed and polished. To delve into the details of the technology, it is worth watching a master class on gilding.

Pencil gilding

Another “home” method is to use a galvanic pencil in which the tip serves as the anode and the surface of the product as the cathode. The principle of deposition is similar to the electroplating method, but the equipment used eliminates the use of a solution bath.

Noble metal not only decorates products, but also performs protective functions. The gilding process should be entrusted to professionals - lack of experience and the use of dangerous components often leads to undesirable consequences.

Contact method- electrolytic gilding without an external current source - allows you to obtain uniform and very dense coatings that adhere quite tightly to the metal surface. Since in this case the “electrolysis” process is carried out as a result of the potential difference between the part and the electrolyte, it is possible to qualitatively gild only brass parts or parts made of other metals, previously coated with a thin layer of brass.

Fig.1. Installation of a bath for electrolytic application of a gold plating layer by contact method:
1 - glass vessel, 2 - ring electrode made of zinc, 3 - glass made of porous ceramics, 4 - copper wire - suspension, 5 - suspension supports - insulator.

Before applying a layer of brass to the surface of a steel product, the product is ground, polished, after which its surface is degreased and etched, that is, subjected to chemical treatment. The first three operations do not require much explanation. Pickling of steel products is carried out in an alkaline solution containing 20 - 30 g/l of potassium oxide hydrate (or sodium hydroxide) and heated to 75 - 85 g. C. The etching time of the product in a hot solution is approximately half an hour, at room temperature the product is kept in alkali for at least 1 hour. After thorough washing in running water, the part is immersed for 1 minute in a 0.5% solution of hydrochloric acid to remove traces of iron oxides from the metal surface. From a solution of hydrochloric acid (again after thorough washing), the part is placed in a bath for electrolytic brass plating, and the sooner the wet part is in the bath, the better the coating will be.

The composition of the electrolyte (plating bath) for brass plating is given below (in g/l):

Copper cionide 30 - 35;
- zinc cionide 8 - 12;
- sodium cyanide 20 - 25;
- sodium carbonate 6 - 8;
- sodium bicarbonate 8 - 12;
- ammonium hydroxide 3 - 5.

The electrolyte components are dissolved in distilled water. Brass plating is carried out at a solution temperature of 25 - 35 degrees C and a current density of 0.3 - 0.5 A/sq.dm. Galvanic cells of type 373 are suitable as a current source. You will also need a rheostat to regulate the current.

The anode is a plate made of M70 brass. To obtain a more uniform coating thickness, the part must be rotated during the electrolysis process. Since the brass layer serves as a sublayer for the subsequent gold layer, it is necessary to build up a layer of brass with a thickness of at least 1 micron, which will take approximately 15 - 20 minutes. Please note that the surface layer of freshly deposited brass is very fragile and should not be touched.

In cases where the brass layer serves as a decorative coating, it is recommended to treat it with a solution of some passivator to increase strength and weather resistance. In our case, the brass layer is an intermediate “product”, so its unpassivated surface only promotes the mutual diffusion of brass and gold, leading to a strengthening of the connection between the layers. Therefore, after thorough rinsing in hot water The brass-plated part is immediately transferred to the gilding bath. Some compositions of baths for contact gold plating are given in the table.

Components, g/l electrolyte I electrolyte II electrolyte III

Gold chloride 0.4 3.5 1.5
Potassium bicarbonate 50 - 100
Sodium chloride - 2 -
Sodium sulfide (crystalline) - 30 -
Iron-sine-containing potassium - 3 -

The temperature of the solution during the gilding process is 70-80 degrees, the time to obtain a gold layer about 0.1 microns thick is: for bath I - 3-5 minutes; for bath II and III - 5-10 minutes. It makes no sense to significantly increase the time the product stays in the bath - when the above-mentioned thickness of the gold layer is reached, the process practically stops and thickening of the gold plating layer cannot be obtained.

Contact gold plating is carried out in an electrolytic installation, a section of which is shown in Fig. As can be seen from the figure, a cylindrical zinc electrode (anode) is placed in a glass container, immersed in an auxiliary electrolyte - a sodium chloride solution (solution concentration 30 g/l). Inside a porous ceramic glass copper wire hang the part that needs to be gilded. The wire is held in the center of the glass by a support (for example, a tube) of insulating material, which is attached to the glass. Thus, the wire does not come into contact with the glass, but is electrically connected to the zinc anode.

In this installation, a glass made of porous ceramics plays the role of a semi-permeable diaphragm, separating solutions of two electrolytes and preventing their mixing, but not creating barriers to the process of electron-ion conductivity. If you don’t have such a glass, a tarpaulin, filtered paper, or even unglued paper will work as a semi-permeable partition. Just keep in mind that when replacing the partition material, you will have to experimentally determine the electrolysis time and adjust the composition of the bath. After gilding, the part is thoroughly washed and air dried. Despite the small thickness of the gold layer, the coating is quite dense, durable and shiny.

Characteristic feature this method gilding is a high adhesion strength of the gilding layer to the base metal, but this indicator, as mentioned earlier, largely depends on the quality of the preliminary preparation of the metal surface for brass plating.

In cases where high adhesion strength of the coating is not required, and the gilding layer is intended for purely decorative purposes, it is better to use the so-called hot gilding method- a method that is less labor-intensive and safer.

For hot gilding, prepare a solution of the following composition (in g):

Nitric acid (density 1.36 g/cc) 20;
- hydrochloric acid (density 1.18 g/cc) 20;
- gold 1;
- antimony chloride 1;
- tin 1;
- boric acid (saturated solution) 20.

The solution is prepared as follows. Nitric and hydrochloric acid are mixed in a glass container and gold is dissolved in the resulting “aqua regia”, after which antimony chloride and tin are added. Next, the dishes are placed in a water bath and after complete dissolution of tin, add to the solution boric acid. It is necessary to work with the solution in compliance with all necessary precautions - the liquid is very aggressive, so contact with the skin is dangerous, and the liquid vapors are toxic (contain nitrogen oxides and chlorine).

The product intended for gilding is first ground, polished, degreased, and also pickled by boiling in alkali. After which the “golden” solution is applied to the washed, prepared surface of the product with a soft brush. When the solution dries, the product is heated in the flame of an alcohol lamp or over a charcoal fire. As a result, gilding is formed that does not require additional processing, but the adhesion of the gilding layer to the base metal is not very strong.

Products made from gold alloys of various grades are used not only as jewelry; parts made from precious metals are also actively used in industry. The use of pure gold in these cases is usually not economically justified; most often, only an external gold coating is required, which gives the element the necessary properties. Surface gilding is one of the main galvanic processes in jewelry, which makes it possible to give the product the required decorative or specifications. How is electroplated gold produced?

Gold plated jewelry

When they hear the word “jewelry,” many fashionistas imagine unremarkable plastic or metal jewelry that carries no value. High-quality costume jewelry cannot be classified as this type of product; even its base is made of cheap material. Craftsmen usually use base metals for the base of jewelry, and to give it an attractive appearance, they apply a beautiful coating using the galvanic method.

Cupronickel, bronze, brass, pewter or nickel silver are used to produce blanks for jewelry. All these alloys differ from each other in color characteristics and properties. Cupronickel is produced by alloying copper, iron, nickel and manganese. The result is an alloy similar in color to silver. Pewter is made from tin, which makes it easy to cast. Nickel silver is an alloy of zinc, nickel and copper, which, depending on the predominant element, acquires a tint of different shades. Bronze and brass contain copper, which makes their color quite attractive.

Craftsmen achieve the golden color and characteristic “precious” shine using electroplating. The base of the decoration does not have to be metal; it can also be a material of a non-metallic nature. During the galvanic process, the product is coated with a layer of gold or silver. IN last years often resort to the rhodium plating procedure.

Electroplating with gold provides the decoration with an attractive appearance. Reviews of such products are divided into two parts. Lovers of good jewelry speak positively, arguing that gold-plated jewelry has the effect of a precious metal, but for less money. High-quality coating and painstaking work of an experienced craftsman can bring the most daring design ideas to life. Others have a negative attitude towards products of this kind, since they only recognize precious jewelry.

Methods of applying gold plating

Among possible options Experts distinguish two methods of applying gold plating: mechanical and electrochemical. The mechanical method involves covering the surface with gold leaf. Gilding with the thinnest sheets of metal has been used since ancient times; over many centuries, the essence of the procedure has remained virtually unchanged. Gold leaf plating can be oil-based or glue-based; in the first case, the metal is glued to oil varnish, and in the second, to polyment. The oil-based coating turns out matte; to achieve the effect of a shiny surface, experts resort to using an adhesive base. Work on creating an adhesive coating can be carried out exclusively indoors, since such gilding is characterized by high sensitivity to moisture.

The electrochemical version of surface treatment with precious metal is a galvanic method of applying gold to a product. What it is? During the work, the master applies, using electric current, a thin layer of yellow precious metal, the size of which can reach fractions of microns.

Like any coating, electroplating has its advantages and disadvantages over other options. There are quite a few advantages of coating obtained in this way. These include a high level of wear resistance, excellent reflectivity, high current conductivity, the ability to protect the product from aggressive external factors, the effects of corrosive and oxidative processes. When applying galvanic coating, the specialist carrying out the work can control the thickness of the precious metal layer. Due to the listed properties, galvanic gilding is widely used both in surface decoration and for creating technical parts of devices.

Electrochemical deposition of gold on the surface.

For a long time, the main disadvantage of the method was considered to be the limited scope of its application. The electrochemical method of applying gold to a surface assumes that this surface is conductive, that is, made of metal. Thanks to scientific advances, this problem has now been partially resolved: special technologies make it possible to gild dielectric materials using conductive varnishes and films.

Gilding technology

Gold plating is a process of depositing a metal film. The thickness of the film can be different; depending on the purpose of gilding, a specialist can apply a layer on the product with a thickness ranging from a fraction of a micron to a fraction of a millimeter. The whole process is divided into three stages: first the surface must be prepared, then a layer of metal is applied and final processing is carried out.

A high-quality coating will only be achieved if the surface to be treated is well prepared. The product is pre-polished mechanically. To do this, use sandpaper, special pastes or grinding machines. Then the surface is degreased in an organic solvent. Alcohol, acetone or gasoline can cope with this task. Another mandatory procedure before galvanic treatment is pickling - removing existing contaminants, oxides and rust from the surface.

Sometimes it is necessary to electroplate only part of a part; for this, the remaining areas of the product must be protected from the effects of electrolyte and gold deposition. To do this, before applying the precious coating, acid-resistant varnish is applied to areas that are not subject to gilding..

The part is plated with gold using galvanic baths. The work is carried out using conductive suspensions and drums made of acid-resistant materials or in bell installations that ensure excellent electrical contact. The galvanic bath must also have an acid-resistant coating so as not to be destroyed under the influence of the electrolyte and equipment in the form of steam jackets. The whole process takes place at high temperature and the required current density, which are supported by automatic regulators. It is almost impossible to carry out galvanic procedures at home, since this requires not only special equipment, but also rare chemical reagents.

Upon completion of the work, the product is coated with a thin metal layer, which provides the best characteristics for the part. For decorative products, it is important to acquire an attractive appearance and the desired shade, for industrial parts - the ability to resist corrosion, improve electrical contact and facilitate the soldering process. Sometimes galvanic coating is used to increase the volume of a product. Depending on what properties need to be imparted to the part, electroplating can be done with both gold and other elements: silver, chromium, nickel.

Gold alloy plating

To coat products, gold alloys are most often used, to which a ligating component is added. An additional element in the alloy allows you to give the details necessary qualities and the desired shade. In Russia, preference is given to gold with a reddish tint; in the USA and some other countries, priority is given to coatings of lemon yellow or brass shades.

In order for electroplating to have a tint not like gold, but like platinum, the working alloy must consist of gold and nickel, the percentage of which must be at least 8-10%. This coating will have a white tint and will also be highly hard compared to a pure gold layer. The higher the proportion of nickel in the alloy, the higher the hardness and wear resistance of the final surface will be. Electroplating based on gold and nickel is used abroad for jewelry. Due to their high resistance to corrosion processes, they can also be used for technical purposes.

An alloy of gold and copper in Russia is used to coat elements wristwatch. The progress of the process depends on the concentration of free cyanide in the electrolyte: the higher the concentration of the substance in the electrolyte, the lower the copper content in the resulting coating. When the process is carried out under conditions of neutral electrolytes, a copper-gold coating with a thickness of 20 microns can be obtained.

In addition to the listed alloys, gold-silver and gold-antimony compositions are also used. The percentage of elements in the final coating depends on the characteristics of the electrolyte and the chemical reagents used.

Gold-antimony electroplating deserved positive reviews due to its use for gilding spectacle frames. A coating of this composition is characterized not only by increased wear resistance, but also by attractive appearance. Depending on the thickness, it can turn out semi-shiny or shiny. Such properties, together with a high level of resistance to mechanical stress, allow the alloy to be used for decorative purposes.

Gilding is an electrochemical process in which a thin layer of gold is applied to metal. Positively charged gold ions are carried by an electric current through a gold plating solution that is applied to a negatively charged metal, typically jewelry. Gold plating is an easy way to give a new look to tarnished jewelry and other metal accessories. Using the gold plating kit and following instructions will make the gold plating process easy and won't take much time.

Steps

Part 1

Buying a gilding kit

Select the metal item you plan to gild. This could be a piece of jewelry, a piece of a wall clock, decorative metalwork, or a car emblem. The type of kit required for gilding depends on the choice of product. Some items, especially larger ones, require the use of a Brush Gold Plating Set, while smaller items such as jewelry may require the use of a Dip Gold Plating Set. Look for similar sets online to see which ones are of the highest quality.

• Most gold-plated jewelry is made with a silver base, but other metals such as copper or aluminum can also be used.
• Silver and gold react with each other, which subsequently causes the item to tarnish. Using copper instead of silver will create a longer-lasting effect since the metal does not react as strongly with gold.

1. Buy a gilding kit. Now that you have decided on the product, you can buy a suitable gold plating kit. If you are still in doubt, contact the set manufacturer or gold plating specialists to find out which set would be more suitable.

   • A standard gold plating kit includes liquid gold solution, electrical supplies, and a gold plating stick or brush. This set is ideal, but for gilding you may also need other solutions and accessories depending on the type of metal or product you are working with.
   • Gold plating solutions typically consist of 14, 18, or 24 karat gold. The color of the finished product will depend on the carat level.
   • Colors may vary when metals such as copper or silver are added.

2. Prepare everything necessary materials for gilding. Although a gold plating kit should have everything you need, this is not always the case. Some gilding solutions must be brought to a certain temperature; in this case you will need a hot plate or heatproof glass. You will also need electricity. If you don't have anything suitable for this in your kit, you will need a 12 amp rectifier and a voltage regulator. At the very end you will also need distilled water.

   Part 2

   Preparing the gilding kit

   1. Prepare a glass and solutions. In addition to the gilding solution itself, your kit should include an activating solution. These solutions do not have to be mixed in one glass. Instead, you can place them opposite each other to make it easier to move the piece from the activating solution to the distilled water and gilding solution without unnecessary risk.

      Start heating the solutions. The solutions do not require constant heat, but they do need to be brought to a certain temperature before gilding, so set them to heat in advance. The exact temperature of the solutions depends on the specifics of the set you purchased, for example, the number of carats. Follow the instructions exactly.

      Install the power source. Even if you are installing the power supply separately from the kit, follow the kit's instructions for installing it.