Stainless steel often requires surface treatment to achieve the desired aesthetic or performance properties. Shot blasting and sandblasting is limited due to the high likelihood of work hardening. Modern production uses pickling of stainless steel, after preliminary thermal or mechanical treatment. The complexity of this process, compared to conventional black, low-alloy steels, is due to the presence of a chromium oxide film that acts as a protective barrier. It is she who forms a hard scale that interacts poorly with reagents. Technological influences may cause color changes on the surface. These include welding, soldering, and other operations associated with high temperatures. Iridescent colors can be removed by etching. Individual pickling methods and compositions have been developed for various stainless steel chemistries, taking into account the influence of the steel elements, in order to achieve maximum results.

prevailing etching methods for stainless steel steels are alkaline and acidic, which can be intensified by electrolysis or proceed without it.

Acid pickling

Maximum effect acid pickling of stainless steel achieved by sequential interaction of the stainless steel surface in baths with two types of acids - sulfuric and nitric. The sequence of stages is as follows

1. Degreasing, removal of large hooks, scale
2. Etching in a sulfuric acid bath (concentration 10-12%) or a sulfuric acid bath (8% sulfuric acid, 4% hydrochloric acid). In this case, corrosion of scale and roughness on the surface occurs. The ideal process temperature is between 60 and 80 degrees Celsius. Control of this parameter is important for process control. The duration of treatment depends on the steel grade, the presence of a controlled ratio, the concentration of acids. If the bath is depleted, pitting corrosion is possible. For example, steel with 18% Cr, 8% Ni requires 23 to 45 minutes of pickling in a sulfuric acid bath. A twofold reduction in processing time can be achieved if this operation is carried out in a controlled atmosphere.
3. Rinsing in plenty of running water
4. Immersion of the workpiece in a bath filled with a solution of nitric acid and hydrofluoric acid (10 - 20, 1-2 weight percent, respectively). At a bath temperature of 60 - 70 degrees, the processing time is 7 - 15 minutes.
5. Repeated rinsing with large volumes of water

The presented method is basic and has many variations. Etching in one nitric acid bath, with an admixture of hydrofluoric acid, increases the etching time to 30 minutes. Sodium fluoride can act as a substitute for hydrofluoric acid. Increasing the concentration of hydrofluoric acid to 10% allows the process to be carried out at low temperatures, avoiding preliminary immersion in sulfuric acid.

Reducing the pickling time in sulfuric acid can be achieved by adding no more than 5% sodium chloride. Such a move gives the desired effect in 15 minutes, but at the same temperature, about 80 degrees Celsius.

Be careful: if it is necessary to perform the procedure, in a room with insufficient aspiration, replace the components of the second stage of etching. Acids emit harmful fumes when pickled. It is proposed to replace the solution of ferrous sulfate (7%) and hydrofluoric acid (2%).

To choose the right acid pickling method, you need to know and take into account the state of the oxide film on the surface of stainless steel. Appearance can suggest the composition of the film. The green color of the scale indicates a high content of chromium oxides. Accordingly, the action of acid media will be difficult and will require more time.

electrolytic etching

One of the options common in modern enterprises is electrolytic pickling. A workpiece or part placed in an acid bath is connected to a positive or negative contact. When current passes through the surface of stainless steel, oxygen is released. The gaseous phase has a mechanical effect on the oxide film. This helps speed up the machining process and the quality of the resulting surface.

Etching with prepared pastes

The modern industry offers a variety of pickling agents on the market. stainless steel paste . Their main purpose is the local processing of welds, the consequences of a change in the uniformity of the surface color under the influence of temperature exposure. The principle of working with such pastes is simple and can be used even in small workshops.

• Applying the paste in a thick layer up to 2 cm, using a brush
• Exposure 60-90 minutes
• Rinse with water jet

The use of pastes is advisable for the treatment of welding seams of stainless steel grades. The processed seam is capable to resist corrosion even in the conditions of a crude car wash room.

alkali etching

Processing the surface of stainless steel with molten caustic soda is called alkaline pickling. It should be noted that during this process, the destruction of the oxide film occurs, while the chemicals do not react with the metal. An increase in temperature contributes to the corrosion of the oxide film, improving the quality of the treated surface. Rapid cooling in the liquid also improves the surface finish.

Achieving 100% results with this type of processing is almost impossible. Residual deposits from chromium oxides, nickel and iron oxides are possible on the metal. Among the recommendations for the final fine-tuning of such defects is a short-term treatment in a nitric acid bath.

Alkaline Etching Methods

There are the following methods

• Extract in soda. The content of sodium nitrate should fluctuate within 20-40%, heated to a temperature of 460-500 degrees Celsius. Etching in such an environment lasts for 15 minutes. Some austenitic stainless steel grades are not allowed to be heated above 450 degrees. This can lead to intergranular corrosion. This is followed by a washing step in a large amount of water, followed by a 5-minute immersion in a sulfuric acid bath and up to 10 minutes in a nitrate bath.
• Known in England, since the first half of the 19th century, the etching method, in combination with the passage of electric current through the etched part. At a current density of 11 A/m2, 15 seconds is sufficient. This reaction rate is related to the electrolysis process. The release of sodium and hydrogen at the cathode contributes to the reduction of oxides. The recovered metal is deposited on the surface. This type of etching allows you to get defatted metal, characterized by purity and uniformity. With this method, soda is used. Variations with the composition and addition of calcium chloride are possible. This method is used for etching flat, rod blanks, drawn products.
• Treatment with sodium hydrides is based on the reduction by exposure to the metal with sodium and hydrogen. The presence of sodium hydride is achieved by the interaction of hydrogen and sodium, which is in a molten state. A cylinder without a bottom plane is placed in molten caustic soda. The top plane has a hole. Sodium is poured into this hole, it reacts on the surface of the bath. A jet of hydrogen is passed through a spot of sodium on caustic soda. A hydride is formed and diffused in the volume of the bath. Achieving the required concentration of 1-2% sodium hydride occurs in controlled thresholds. In the absence of an air separation product, dissociated ammonia is used. Parts are heated in such a bath to 400 degrees Celsius. Stainless steels show good pickling results with this technique and a duration of 4-17 minutes. After etching, it is recommended to thoroughly rinse the parts. If necessary, carry out additional treatment in a nitric acid bath. With the high cost of this method, its obvious advantage is the fact that the metal does not interact with the etchant. Metal loss is minimal. The lower process temperature reduces the cost of coolant and the safety of operations.

There are certain rules, the implementation of which is mandatory for any of the presented methods. Among them, the priority treatment of the metal surface before etching, removal of the oxide film, degreasing. The etching process is equally important.

Bath materials

Choosing the right material for pickling baths is a difficult task for chemists and materials scientists.

• covered with ceramics
• glass covered brick
• wood, lead-coated concrete
• rubber derivatives
• certain stainless steel grades for acid baths.

The content of nitrous acid with impurities of hydrofluoric or hydrochloric acid allows the use of the same materials. The only exceptions are lead as a coating, ceramics with a high silicon content, due to their interaction. The use of steel is quite possible for use in alkali baths, monitoring the flow and intensity of electrolysis in close proximity to the material. Under certain conditions and acid content, its temperature, nature, it is possible to use stainless steel grades for pickling tanks. Such, for example, as 8X18H8M or 10X20H25M4.

From the information provided in this review, it can be concluded that the treatment mode, the chemical composition of the bath, the need for additional mechanical treatment, the use of electrolysis should be determined based on specific initial conditions (steel grade, oxide film condition, technological capabilities) and adjusted in the context of the expected end result. .

Etching is a metal treatment process, as a result of which a layer of a certain thickness is removed from the surface under the influence of active chemicals (acids or salts with an acidic reaction), as well as direct current in an electrolyte bath.

Metal pickling can serve a variety of purposes and can be used in industry and at home. The surface of the product subjected to etching receives a number of technological and decorative properties and allows you to examine its microstructure in a metallographic microscope, remove scale and other non-metallic inclusions from the surface, obtain the necessary jewelry ornament or prepare for soldering.

Etching, also called electrochemical engraving, is most often used at home or in the garage to obtain relief images on various objects with decorative functions. Most often, steels with high hardness are subjected to it, the processing of which with a conventional engraving tool requires a lot of effort. This process is not very difficult even in the absence of artistic skills, if you follow its technology.

Metal surface preparation

In order for the etching process to proceed at a high speed, and the thickness of the removed layer to be the same, all dirt and traces of oils should be removed from the surface of the product. For this, ordinary detergents and cleaning products used for washing dishes and warm water are suitable. After washing and drying, the surface should be wiped with a fiber soaked in a solvent, which, in addition to degreasing, helps to remove moisture residues.

Separately, it should be said about the quality of surface treatment. Mirror polishing is guaranteed to give a good contrast pattern even at a small etching depth. But if its implementation is impossible for any reason, the surface can be treated with sandpaper so that the risks from it go in one direction. It will also give a good optical effect.

drawing

To apply a pattern to a metal, you can use a lot of different methods that work according to the same mechanism: areas that are not subject to etching are protected from exposure to an aggressive environment or electrolyte.

Method number 1

The most affordable way is to apply ordinary nail polish to the protected areas. However, it has a number of significant disadvantages:

• The viscosity of the varnish does not make it possible to make the lines thin enough to obtain patterns of high complexity;
• Good ability in fine arts is required;
• Correcting inaccurate lines is difficult.

Method number 2

First you need to apply a protective layer on the entire surface of the product. To do this, you can use primers GF-021, XV-062 or bituminous varnish, available in auto parts and household goods stores. After the coating has completely dried, using a gel pen or a thin marker, you can apply the contours of the future image. For this task, you can attract an experienced artist.

Further, from a copper (possibly brass) wire or rod, the diameter of which is selected based on the convenience of holding in the hand, it is necessary to make a needle with a pointed end and scratch the primer along the image lines to the metal. Harder needle material may damage the polished surface of the item.

Already at this stage, it is possible to assess the relief of the future ornament. To obtain areas with different depths of metal etching, for example, contours and penumbra, this process can be carried out in two or more cycles.

Important! In the process, the primer should not chip off. Before drawing a picture, it is worth experimenting and making sure that it is suitable for work.

Method number 3

You will need a laser printer, glossy paper, imaging software, and an iron. The selected image must be formatted (fit to size, made mirrored) and printed. The most affordable source of glossy paper is women's magazines.

The printed image is applied to the surface, covered with a regular landscape sheet on top (to protect the iron) and ironed. After cooling, the paper is washed off under running water, and the toner layer remains on the metal surface.

This method is often used for etching printed circuit boards. Its main drawback is that the pattern is applied only to a straight surface.

Important! Gloss underwater is hard to see. After drying, you need to make sure that it does not remain on the product.

Care must be taken to protect all surfaces of the product. To do this, you can use various substances. You can close the back surface with ordinary plasticine: it is a good dielectric.

Metal etching methods

The choice of a particular method depends on many factors: the chemical activity of the metal, the availability of chemical reagents and safety considerations.

chemical etching

It is carried out in a container with an active substance. For carbon steels, solutions of weak acids can be suitable: citric, acetic. Hydrochloric acid works well. Etching in battery electrolyte, nitric acid and rust converter should be treated very carefully: toxic gaseous substances can be released during the process, so it is better not to work with such reagents in the absence of a fume hood and good ventilation.

One of the safest substances is a saturated solution of ferric chloride. It can be bought in stores selling radio components. The advantages of the solution are its practically unlimited service life (when working with iron alloys) and the staining of the etched surface in an even gray color.

The duration of the process is selected experimentally depending on the concentration of the reagent used and the activity of the metal.

Electrochemical etching

Many stainless and acid-resistant steels, for example, 40X13, 95X18, 08X10H18, 03X12H14M2, do not react to acids, so an electrochemical method is used to pickle them.

For it, you will need a plastic or glass electrolyte bath, wires, terminals and a direct current source. A saturated sodium chloride solution will do as an electrolyte. When choosing a container for it, it should be remembered that the process can proceed quite rapidly, so its volume should be 2 times larger than that of the electrolyte.

Batteries can be used as a current source, but it is better to use a charger (3 - 10A) with an ammeter and the ability to adjust the current parameters to select their optimal value. The workpiece is connected to the anode (positive contact) with the help of terminals and a conductor; any stainless plate placed in the bath parallel to the front surface of the workpiece can be used as a cathode. After that, the device is connected to the network.

The whole process can take from two minutes to half an hour, depending on the current strength and the area of ​​\u200b\u200bthe pattern. The etching depth should be controlled by periodically removing the part from the bath. In this case, do not forget to turn off the power.

At the end of the process, the protective coating can be removed with a suitable solvent and the results of the work evaluated. Due to the good adhesion of the etched surface, it is possible to create a colored pattern.

To do this, the entire surface of the product is blown from a balloon with nitro enamel, and after it dries, it is wiped with a piece of clean leather, felt or other non-abrasive material. The paint is removed from the polished surface, leaving only in the depressions.

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Chemical solutions for pickling iron and steel

The simplest effective pickling solutions for iron and steel parts are dilute inorganic acids, especially 20% sulfuric acid, in which pickling is carried out at 45-50 ° C, or 20-25% hydrochloric acid, in which parts are pickled at room temperature. For etching, 10-15% phosphoric acid is also used, heated to 60-70°C. Parts are etched in it, which will then be varnished or their surface will be left without further processing. If a galvanized surface coating is provided after pickling, then this bath is unsuitable.

Chemical etching of non-ferrous metal surfaces

Etching copper and brass

On brass, the solution forms a light yellow coating, on copper - light pink. The solution contains:

Nitric acid concentrated 250 ml;
- Hydrochloric acid concentrated 150 ml;
- Ethyl alcohol denatured 100 ml;
- Water 500 ml.

Parts are poisoned by briefly immersing them in a bath with a solution, after which they are removed and immediately washed with water.

Matt etched copper

After etching on copper, a rough (to matte) surface will be obtained. Bath composition:

Nitric acid 40% 600 g;
- Sulfuric acid concentrated 400 g;
- Sodium chloride 3 g;
- Zinc sulfate 2 g.

Brilliant etching of copper and its alloys

Sulfuric acid concentrated 500 ml;
- Nitric acid concentrated 500 ml;
- Hydrochloric acid concentrated 10 ml;
- Soot 5 g.

The operating temperature of the bath is 18-20°C. Fat-free parts are immersed in a bath with a solution for 10-30 seconds, after which they are removed, washed with water and dried.

Pickling solution for aluminum and its alloys

The aqueous solution contains:

Sodium fluoride 40 g/l;
- Caustic soda 50 g/l.

The operating temperature of the bath is 70-80°C, the processing time is about 1 minute.

Another aqueous solution contains

Chromium oxide 30 g/l;
- Sulfuric acid concentrated 150 g/l;
- The working temperature of the bath is 70°C, the processing time is 1-1.5 minutes;

The simplest way of decorative painting of steel products

Electrochemical method can be used to paint steel products in any color. If the paint layer is varnished, it will reliably protect the product from corrosion. The composition of the solution in which steel products are painted includes the following components:

Copper vitriol 60 g;
- Refined sugar 90 g;
- Caustic soda 45 g;
- Water up to 1 liter.

Copper sulfate is dissolved in 200-300 ml of distilled water, then sugar is added to the resulting solution. Separately, caustic soda is dissolved in 250 ml of water and a solution of copper sulphate with sugar is added to it in small portions (with stirring). After mixing these two solutions, add distilled water to 1 liter. The part is cleaned, polished and degreased in a solution used in nickel plating, and then thoroughly washed in warm water. An additional electrode is made from red copper (preferably grades M0, M1). The part and the electrode are connected to a battery from a pocket flashlight (or other 4-6 V DC source), and the copper electrode must be connected to the plus of the battery, and the part to the minus. The copper electrode is first lowered into the solution, and then the part. After 5-10 seconds, the battery is disconnected, and staining continues without electric current. Being in the solution from 2 to 25 minutes, the part is painted in the following colors (in the order of their appearance): brown, violet, blue, blue, light green, yellow, orange, red-lilac, greenish-blue, green, rose-red . The item can be taken out of the solution (checking the color) and lowered into the solution again - the process will proceed normally. When holding the part in the solution for more than 25-30 minutes, the process is cyclically repeated many times.

As the electrolyte evaporates, distilled water is added to the bath, since an increase in the electrolyte concentration worsens the quality of the color. To obtain more contrasting colors, 20 g of sodium carbonate (anhydrous soda) must be added to the finished electrolyte. If the coloring turned out to be unsuccessful, the film can be easily removed by wiping the part with ammonia. The painted parts are washed with water, dried and coated with a colorless varnish.

A simple way to decoratively finish an aluminum surface with a mother-of-pearl effect

The aluminum surface is cleaned with a metal brush, making small strokes in different directions (creating a certain pattern). Chips and dirt are removed from the surface with a clean rag. A clean aluminum surface is covered with an even layer of 10% sodium hydroxide solution (working temperature of the solution is 90-100°C). After the solution dries, a beautiful film with a pearly sheen forms on the aluminum surface. For better preservation, the film is covered with a colorless varnish. A more beautiful film is obtained if, before applying a solution of caustic soda, the product or part is heated to 80-90 ° C.

Chemical way of clarification of products and details from silumin (restoration)

Products and parts made of silumin (an alloy of aluminum with silicon) are quickly covered with an oxide film of dark tones. However, they can be shiny for a long time if they are lightened. Products or parts are cleaned and, if necessary, polished, then degreased, washed and immersed for 10-20 minutes in the following solution:

Chromic anhydride 100 g;
- Sulfuric acid concentrated 10 g;
- Water up to 1 liter.

The working temperature of the solution is 18-20°C.

After clarification, the products and parts are washed and dried, and so that the surfaces of products and parts do not oxidize for a long time, they are covered with a colorless varnish.

What you need to know about polishing steel and non-ferrous metals

Polishing is used to improve the cleanliness of the surface of parts, devices, to eliminate traces of previous processing on them (strokes, scratches, small dents and the smallest irregularities). There are two types of polishing - preliminary and final. Pre-polishing is used to mechanically remove surface irregularities with loose abrasives (in a free state) or grains fixed on the working surface of the polishing wheel. The final polishing is carried out with fine grinding powders or soft elastic wheels coated with fine polishing pastes. The finest surface finish is achieved by rubbing a piece of felt or woolen cloth lubricated with a special metal polishing paste. After polishing, the surface acquires a mirror finish.

Lime paste is used for polishing nickel, brass, aluminum and other metals, its composition (in%) is as follows:

Vienna lime 71.8;
- Ceresin 1.5;
- Stearic acid 2.3;
- Solidol T 1.5;
- Turpentine 2.2;

The composition of the paste (in%) for polishing steel and other metals:

Paraffin 20;
- Stearin 10;
- Technical fat 3;
- Micropowder M50 67;

Note

Waxy and liquid materials are mixed and heated in a water bath (or over low heat). Then the dry ingredients are mixed into the hot mass.

GOI pastes are designed for polishing steel and other metals and are chromium oxide mixed with waxy substances. Pastes are produced in three grades: coarse, medium and fine. In the absence of chromium paste, oil paint chromium oxide diluted with kerosene can be successfully applied. Crocus paste (iron oxide) is sold in stores ready-made (in dentures, it is used under the name "paste for gold"). Crocus paste is used for polishing brass, bronze, silver and other metals. Powder "Shine", diluted with machine oil, is used for fine polishing of metals.

Chemical polishing of metals

Metals can be polished chemically, i.e. by simply immersing the part or object in a bath of polishing solution without the use of electric current. For this purpose, you can use porcelain glasses or trays. The polishing solution consists of the following substances:

Phosphoric acid concentrated 350 ml;
- Nitric acid concentrated 50 ml;
- Sulfuric acid concentrated 100 ml;
- Sulphate or nitrate copper 0.5 g.

The operating temperature of the bath is 100-110°C. Polishing time from 0.5 to 4 min. When polishing, suffocating fumes are released, so the bath should be in a fume hood or outdoors.
This solution polishes aluminum and its alloys well. It is also suitable for polishing other metals, but the operating conditions (polishing time, temperature) must be different.

CHEMICAL TREATMENT OF METALS

Chemical nickel plating of steel, copper, brass and bronze products
Parts made of steel and copper alloys can be electroplated with nickel. Such a coating not only protects parts well from corrosion and gives them a beautiful appearance, but also has increased wear resistance. The advantage of chemical nickel plating is also that nickel is evenly deposited on all, including internal, surfaces of parts.
The part to be nickel-plated must be properly prepared: sanded, polished and degreased. Steel parts are degreased in a solution containing 20-30 g of caustic potassium (or caustic soda), 25-50 g of soda ash and 5-10 g of liquid glass (silicate glue) per 1 liter of water; copper - in a solution containing (for the same amount of water) 100 g of trisodium phosphate and 10-20 g of liquid glass. Before nickel plating, copper parts must be held on the iron for 0.5-1 min. It should also be borne in mind that alloys containing more than 1-2% lead or cadmium are not amenable to chemical nickel plating.

Degreasing of steel and copper parts at room temperature ends after 40-60 minutes, at a temperature of 75-85°C - after 20-30 minutes. Then the part is thoroughly washed in running water and immersed for 0.5-1 min in a 5% hydrochloric acid solution to remove the oxide film, after which it is washed again in water and immediately transferred to the nickel plating solution. In 1 liter of water heated to 60°C, dissolve 30 g of nickel chloride and 10 g of sodium acetate. Then the temperature is brought to 80 ° C, 15 g of sodium hypophosphate are added - and the solution is ready. A part is immersed in it, the temperature is raised to 90-92°C and maintained at this level until the end of the nickel plating process. At lower temperatures, the rate of the process slows down sharply, and when heated above 95°C, the solution may deteriorate.

The required amount (volume) of the solution depends on the area of ​​the nickel-plated part. The ratio of this area (in square decimeters) to the volume of the solution (in liters) should be in the range of 2.5-3.5.
So, for example, at S/V=3 for 1 hour the thickness of the nickel layer will be 10 microns.

The chemicals used are not toxic, degreasing and nickel plating are not accompanied by the release of harmful gases.
Chemical copper plating of steel and cast iron parts

Quite easily, copper is chemically deposited on iron, steel and cast iron. The coverage is satisfactory.

To coat these metals, a solution is made up of the following substances:

Sulphate copper 8-50 g;
- Sulfuric acid concentrated 8-50 g;
- Water up to 1 liter.

Operating temperature 18-20°C. After thorough cleaning and degreasing, the parts are immersed for a few seconds in the solution. The parts coated with copper are removed from the solution, washed with water and dried.

Chemical chromium plating of metals

Parts made of steel, copper and brass are chemically chromium-plated in a solution containing:

Chromium fluoride 14 g;
- Sodium hypophosphate 7 g;
- Sodium citrate 7 g;
- Glacial acetic acid 10 ml;
- Caustic sodium (20% solution) 10 ml;
- Water up to 1 liter.

Operating temperature around 80°C. Cleaned and degreased parts are metallized within 3-8 hours. In case of chemical chromium plating of steel objects, it is recommended to chemically copper them first. Parts with a deposited chromium layer are washed in water and dried.

Chemical nickel plating of metals

The nickel plating solution consists of the following substances:

Nickel-ammonium sulphate 50 g;
- Ammonium chloride 40 g;
- Water up to 1 liter.

A small amount of metallic zinc is added to the solution and continuously stirred.

Chemical coloring of pewter products in bronze color

Tin products are well painted in bronze color by a chemical method. Products are immersed in a solution or wiped with a cloth soaked in a solution consisting of the following substances:

Sulphate copper 25 g;
- ferrous sulfate ferrous 25 g;
- Water up to 500 ml.

Then the product is dried, brushed, wiped with a cloth and again immersed in a solution consisting of the following substances:

Acetic acid copper 100 g;
- Acetic acid 10% 400 ml.

After that, the product is dried. If desired, it can be polished and covered with a transparent varnish.

"Gilding" of brass

Brass and products from it in the air quickly fade and oxidize. To protect polished items from oxidation, brass parts are often coated with a special golden lacquer. A simpler and more affordable method is as follows: after thorough cleaning and polishing, the brass part is immersed in a 10-15% solution of some kind of alkali to remove fats from its surface. Then the part is washed in water and dipped in a weak (2-3%) solution of sulfuric or hydrochloric acid for 1-2 seconds. Good results are obtained if brass is immersed in a solution of sodium bisulfite, then washed in water and immersed in a solution of copper acetate, heated to 36-40 ° C.

Depending on the time during which the part is in solution, brass is painted from a light golden color to the color of pure gold and even to a reddish-violet hue. The color of the color is monitored by removing the part from the solution from time to time. After painting, the part is washed with water and dried in air. The color is permanent and does not change over time. Acetic acid copper is commercially available, but you can cook it yourself. To do this, dissolve 5 g of copper sulfate in 0.5 liters of water, then mix with a solution of lead acetate (pharmacy lead lotion or lead sugar).

The second solution is made up of 8 g of lead acetate and 0.5 l of water. When the solutions are mixed, lead sulphate precipitates, and copper acetate remains in the solution. This solution will serve as the working solution. The precipitate can be filtered off or left at the bottom of the vessel.

Coloring copper under gold

4 g of caustic soda and 4 g of milk sugar are dissolved in 100 g of water, boiled for 15 minutes, then, with constant stirring, 4 g of a solution of saturated copper sulfate are added in small doses. Well-cleaned copper products are immersed in the hot mixture. Depending on the duration of action, they acquire a different color - from gold, green to complete black.

Golden lacquer for brass (brass passivation)

When brass is passivated, a stable protective film is formed, similar to gilding. This film is not afraid of moisture, so anglers passivate brass spinners. The cleaned, polished and degreased part is dipped for 1 s into a solution prepared from 1 part of nitric and 1 part of sulfuric acid, and immediately transferred to a strong solution of potassium dichromate (chromic acid) for 10-15 minutes.

After that, the part is washed and dried.

Chemical staining of brass

The cleaned, degreased and washed part is immersed in one of the following solutions.

1st solution:

Hyposulfite 11 g;
- Lead sugar 39 g;
- Water up to 1 liter.

Solution temperature 70°C.

2nd solution:

In 250 ml of boiling water dissolve 10 g of caustic soda and 10 g of milk sugar. Then, stirring continuously, add 10 ml of a concentrated solution of copper sulphate to the solution.

Within 3-10 minutes, the part, which is in one of the solutions, turns golden, bluish, blue, purple and, finally, iridescent.

When the desired color is obtained, the part is taken out, dried and polished with a cloth.
Brass acquires a bluish-black color when the prepared part is immersed for 1-3 minutes in the following solution:

Ammonia (25% ammonia) 500 ml;
- Bicarbonate (or carbonate) copper 60 g;
- Brass (sawdust) 0.5 g.

After mixing the components, the solution is vigorously shaken 2-3 times, after which the part is immersed in it.
Brass turns brown when the part is immersed in one of the following solutions.

1st solution:

Hyposulfite 50 g;
- Copper vitriol 50 g;
- Water up to 1 liter.

Solution temperature 70°C.

2nd solution:

Sodium sulfide 100 g;
- Water up to 1 liter.

Solution temperature 70°C.

3rd solution:

Acetic lead 30 g;
- Hyposulfite 90 g;
- Water up to 1 liter.

The temperature of the solution is 80-90°C.

To prepare the 3rd solution, you need to dissolve both substances separately in half the volume of water, then drain them together and heat to 80-90°C. After painting, the part is washed with warm water, dried and covered with a colorless varnish.

The easy way to silver

As a silvering composition, spent hyposulfite (fixer) is used, which is no longer suitable for fixing photographic films or photographic paper. The method is extremely simple. The copper part is cleaned to a shine, boiled in a soda solution and washed thoroughly with water. Then immersed in used hyposulfite. After a while, silver will settle on the part. After washing with water, the part is dried and polished with a cloth. The quality of silver plating and the adhesion strength of silver to copper depends on the concentration of silver in the hyposulfite solution.

Silver plating of metal parts in a hot way

This method can be used to silver any metal. It consists in the following: a cleanly processed part is immersed on a zinc tape in a boiling solution consisting of the following components:

Iron-cyanogen potassium 120 g;
- Potash 80;
- Silver chloride 7.5 g;
- Distilled water up to 1 liter.

The silvering process ends after the complete coverage of the surface of the part with silver. The part is then removed from the solution, washed and polished. It should be remembered that when the solution boils, harmful substances are released, so boiling should be done in the open air or under a hood.

Chemical silvering

1. Several sheets of "Unibrom" matte photographic paper are cut into pieces and dipped into a solution of fixing salt (salt is diluted in the volume of water indicated on the package).

The cleaned and degreased part is placed in this solution and rubbed with an emulsion layer of paper until a dense layer of silver forms on the surface of the part. After washing in warm water, the part is wiped with a dry cloth.

2. Add 1-2 ml of ammonia and 2-3 drops of formalin to 300 ml of spent fixer (remaining after printing photos) (the solution is stored and handled only in the dark).
The cleaned and degreased part is placed in the solution for 0.5-1.5 hours, then washed in warm water, dried and wiped with a soft cloth.

Silver Paste

Parts made of copper, bronze, brass, copper-plated iron can be silver plated with pastes.

1. Silvering paste is prepared as follows: in 300 ml of distilled water or water obtained from the ice of household refrigerators, dissolve 2 g of silver nitrate (lapis) and add a 10% sodium chloride solution to the solution until precipitation stops silver chloride precipitate. This precipitate is washed 5-6 times in running water. Separately, 20 g of hyposulfite and 2 g of ammonium chloride (ammonia) are dissolved in 100 ml of distilled water. Then silver chloride is added in small doses to the resulting solution until it stops dissolving. The resulting solution is filtered and mixed with finely ground chalk to the consistency of thick sour cream. The previously degreased part is rubbed with paste using cotton wool or gauze until a dense layer of silver forms on its surface, after which the part is washed with water and wiped with a dry rag.

2. The polished and degreased part is rubbed with a cloth or a piece of soft leather, on which a paste of the following composition is applied:

Silver chloride 6 g;
- Table salt 8 g;
- Acid potassium tartrate (tartar) 8 g.

The listed substances are ground in a mortar and stored in a dark container; before use, the mixture is diluted with distilled water until a liquid paste is obtained. When the part is covered with a layer of silver, it is washed in water and rubbed to a shine with a soft flannel.

3. Silvering paste is prepared as follows: pour 2 g of ammonia, 4 g of tartar and 1 g of silver nitrate (lapis) into a vessel, add a little distilled water until a semi-liquid slurry is obtained. Then, with a cloth coated with paste, the polished and degreased part is rubbed to a silver sheen.

Chemical method of silvering non-metallic materials

Non-metallic parts, such as plastics, glass, ceramics, wood, etc., can also be metallized chemically. The solution given below for silvering non-metallic materials gives very good results, especially when metallizing glass (silvering mirror surfaces, vessels, bulbs of incandescent lamps, reflectors for projection equipment, etc.).

The composition of the bath for silvering includes the following substances

Composition A

Silver nitrate 12 g;
- Ammonium nitrate 18 g;

After complete dissolution of the substances, the solution is topped up with distilled water to 750 ml.

Composition B

Caustic soda (chemically pure) 19 g.;
- Distilled water 500 ml.

After complete dissolution of caustic soda, the solution is topped up with distilled water to 750 ml.

Composition B

Sucrose 12.5 g;
- Tartaric acid 1.5 g;
- ode distilled 125 ml;

The solution is boiled for 20 minutes, and then topped up with distilled water to 500 ml.

All solutions are stored separately in dark vessels with ground stoppers.

The solution for silvering is obtained by mixing compositions A and B, to which composition C is added immediately before silvering. The parts intended for silvering are thoroughly cleaned in a hot soda solution, rinsed with running water and immersed in a bath with a freshly prepared solution. The working temperature of the solution is 18-20°C. Silvering time - 10 min. The plating can be carried out two or three times in succession, but each time in a fresh solution. Silver-plated parts are dried at a temperature of 50°C for 1 hour, and at a temperature of 18-20°C - for 24 hours. From glass, porcelain or ceramics, the silver layer can be easily removed with nitric acid.

Coloring silver items purple chemically

Silver or silver-plated objects turn purple in a solution consisting of the following substances:

Sodium sulfate anhydrous 12.5 g;
- Sodium carbonate 5 g;
- Water 500 ml.

The solution is heated to 80°C and the object is immersed in it for a few seconds. The item is then allowed to dry. The surface of the object can be coated with a transparent varnish.

Chemical solution for dyeing silver items black
Silver or silver-plated objects turn black after boiling them in a solution of sodium sulphate (100 g per 500 ml of water). After boiling in this solution, the objects are dried and covered with a transparent varnish.

Hot gilding of metal products

In a glass vessel, 20 g of nitric acid and 20 g of hydrochloric acid are mixed. 1 g of gold is dissolved in this mixture. When gold dissolves, 1 g of antimony chloride and 1 g of pure tin are added to the solution. The vessel with the solution is placed in hot water and boiled until the tin dissolves, after which 20 g of a saturated solution of boric acid are added. Products intended for gilding are cleaned, polished and boiled in a solution of caustic potassium or sodium hydroxide. The solution is applied to the product with a brush; the dried product is heated on the flame of an alcohol lamp or on a charcoal fire. After heating, a good gilding is obtained, which does not require polishing. Store the solution in a glass vessel with a ground stopper in a dark place.

Gold plating without an external current source Contact gilding is used to obtain very dense and uniform coatings, characterized by high adhesive strength, and if a large coating thickness is not required. Electrolysis by this method does not need an external current source. The potential difference necessary for the deposition of gold is created by a galvanic cell, in which the coated item serves as the cathode, immersed in the gilding electrolyte, and the anode is a zinc plate, which is in a concentrated sodium chloride solution and connected to the item with a wire, as shown in Fig. 1. For electrolysis, any heated gilding electrolyte from those indicated in the table can be used.

Gilding by immersion is based on the creation of a potential difference at the boundary of the surface of the coated metal and the electrolyte layer adjacent to it. Good quality coatings are formed only on brass or brass-plated parts. Therefore, details from other metals are preliminarily brassed (minimum layer thickness 1-2 microns). The gilding process automatically stops when a layer of gold with a thickness of about 0.1 microns is obtained, but the coating is dense, glossy and has good adhesion to the surface of the parts.

Compositions of solutions and modes of operation during gilding by immersion

Removal of poor quality gold plating

To remove poor-quality coatings, gilded silver items are suspended as anodes in a 5% hydrochloric acid solution at a temperature of 18-20°C. Iron or lead plates serve as cathodes. Anode current density 0.1 - 1 A / dm?. Copper pendants. In addition, the gold coating can be removed in the "royal vodka". "Aqua regia" is a mixture of acids (50% nitric acid mixed in 50% hydrochloric acid). The mixture is used for etching copper, brass, iron, steel, zinc, etc. This solution acts on metals almost instantly; corrosion and dirt disappear, and the surface of the metal becomes shiny or, more often, matte. Jewelers use this mixture to determine pure gold.

Note

When using active acids, safety rules must be strictly observed. It should be remembered that when diluting an acid with water (for example, sulfuric acid), it is necessary to pour the acid into the water, and not vice versa, otherwise the acid will splash, which can lead to severe burns.

Simple ways to extract silver from spent hyposulfite (fixer)
Only a part of the silver contained in the photosensitive layer of the photographic material is spent on the construction of a photographic image. Most of the silver goes into the fixer and developer and can be isolated and collected.

1st way.

Allows you to highlight pure silver. It consists in the following: iron shavings or small iron nails, well washed from fat with gasoline, are poured into a vessel with an exhausted fixer. The solution is shaken from time to time. After 7-10 days, the solution is drained and the nails are dried in air. The silver deposited on the nails crumbles as a black powder, which can then be smelted into ingots.

2nd way.

The depleted fixer and an equal volume of spent metholhydroquinone developer are poured into one vessel. A 30% sodium hydroxide solution is added to the resulting mixture at the rate of 100 ml for each liter of used fixer. Silver is deposited in the form of the finest pure silver powder. The process takes at least 48 hours.
The silver precipitate formed during this time is filtered off and dried. The remaining aqueous solution of sodium thiosulfate, i. fixer, can be reused in work.

3rd way.

A polished sheet of brass is placed in the spent fixer, which is in a glass vessel. After 48 hours, almost all of the metallic silver from the depleted solution will settle on it. After precipitation, the sheet is washed well with water and dried. Then a layer of silver is carefully scraped off its surface.

4th way.
To 1 liter of the used fixing solution add 5-6 g of sodium hydrosulfite and 5-6 g of anhydrous soda. After 19-20 hours, metallic silver formed in the form of a black fine powder is filtered, and the silver-free fixing solution is acidified with sodium bisulfite and reused for work.

5th way.
To do this, prepare a 20% solution of sodium sulfate and pour it into the spent fixer at the rate of 20 ml of the solution for each liter of fixer. After thoroughly mixing the solution, it is allowed to settle for a day. The solution is then decanted from the precipitate, and the precipitate is dried on paper. The precipitate is silver sulfide. Precipitation is carried out in the open air or with enhanced ventilation, to reduce the release of hydrogen sulfide, the spent fixing solution is first alkalized.

PAINTING OF METALS

Coating of metal with varnish "moiré"
Before coating with "moire" varnish, the surface of the metal part is degreased by heating in an oven (oven) for 15-20 minutes at a temperature of 80-100 ° C, then primed with heat-resistant enamel, puttied with varnish putty and dried. When the part dries well, it is treated with pumice stone with water and sandpaper, wiped dry, covered with an even layer of moire varnish with a spray gun and placed for 10-15 minutes in an oven with a temperature of about 80 ° C.

The pattern of the pattern depends on the thickness of the coating and the duration of the heating of the part. When a pattern is formed on the part, it is taken out of the oven for a short time for partial cooling, and then placed back in the oven for the final drying of the varnish. At a temperature of 120-150°C, the varnish dries completely within 30-40 minutes, and at a lower temperature - within 2-3 hours.
To protect the painted surface from dusting, it is covered with celluloid varnish: celluloid is dissolved in acetone to the consistency of liquid oil varnish and applied to the surface in an even layer with a swab. After the acetone dries, a strong protective film remains on the surface.

A resistant coating is obtained if BF-2 glue is added to the aluminum paint. Glue BF-2 is dissolved in alcohol until the thickness of the enamel, then dry aluminum powder is poured into the resulting solution and thoroughly mixed, after which alcohol is added again until normal viscosity is obtained.

The paint prepared in this way fits well when painted with a brush or with a spray gun, it does not crumble and retains its appearance for a long time.

Painting of steel products under aluminum

To give steel products a beautiful look and protect them from corrosion, the metal is often coated with aluminum paint - varnish with aluminum powder. To do this, 15 g of the powder is poured into a colorless nitrolac diluted with acetone (110 g).
In the same proportion, the paint can be diluted not in nitro-lacquer, but in celluloid glue - acetone, in which 5-10 g of x-ray film, cleaned of emulsion, is dissolved.
The surface of the product is pre-cleaned thoroughly and then a thin layer of paint is applied using a spray gun.
A resistant coating is obtained if BF-2 glue is added to the aluminum paint. Glue BF-2 is dissolved in alcohol until the thickness of the enamel, then dry aluminum powder is poured into the resulting solution and thoroughly mixed, after which alcohol is added again until normal viscosity is obtained. The paint prepared in this way fits well when painted with a brush or with a spray gun, it does not crumble and retains its appearance for a long time.

What you need to know about paint incompatibility and the perception of paint color

All paint components are chemicals. Metals (copper, zinc, aluminum), which are part of paints in the form of powder, affect the corrosion of the painted metal surface and the binder. Metal oxides and salts affect the binder, accelerating film formation. Dissimilar types of binder cannot be combined with each other, and some oil paints obtained on the same binder, but based on different pigments, cannot be mixed.

Pigment incompatibility. When mixing pigments, it is very important to take into account the nature of their interaction. In case of incompatibility of pigments, their destruction and loss of anti-corrosion properties occur.
When mixing paints with incompatible pigments, their color is lost.

Binder incompatibility. Oil paints can only be mixed with oil paints (on a homogeneous basis), glyptal paints with glyptal paints, pentaphthalic paints with pentaphthalic paints, epoxy paints with epoxy paints, bituminous varnishes with asphalt and coal tar varnishes, etc. However, all thick oil paints can be diluted with drying oils and varnishes made on the basis of only light natural and artificial resins, excluding asphalt and bituminous resins.
Incompatibility of paint with surface material. All primers without exception can be applied to the steel surface: oil, phosphating, protective, glyphthalic, phenol-formaldehyde, on vinyl chloride copolymers, ethinol, acrylic, etc.

Select the image you want to etch on the steel. You can draw the image by hand or reproduce an existing image on the surface of the steel. Depending on the transfer method you choose, you can end up with either a very simple pattern or a rather complex one.

• If you are planning to replicate an existing pattern, then choose something with a high contrast of black and white.
• If you plan to make and sell prints of your etched patterns, please select a public domain image or obtain permission from the copyright owner, if they exist.

Transfer your pattern to the surface of the steel. You can translate the pattern in one of the following ways. However, keep in mind that regardless of the method of transfer, it will turn out to be the opposite of the image obtained when etching on steel. If you plan to use the etched plate solely as decoration and not for printing with it, then this will not matter to you.

• The oldest method of translating images is to coat the steel with liquid varnish or a waxy substance (such as beeswax), or even enamel paint or nail polish. This coating is called ground. You can scratch your image directly into the ground with needles or cutting tools. (This process is similar to carving wood.) The primer will act as a resist, isolating the areas of steel covered by it from the action of the pickling acid.
• Another method is to cover the surface of the steel with permanent marker marks in places you don't want to etch. To determine the best resist, you will need to experiment with several different brands and colors of permanent markers.
• A third method is to create a stencil that is transferred to steel with an iron, either by photocopying the image onto transfer paper or by printing it onto glossy photo paper with a laser printer. Lay the paper on the surface of the steel with the image down and set the iron to high temperature, smooth it in smooth circular motions for 2-5 minutes. (If you're using transfer paper, press gently on it, and if you're using photo paper, push the iron firmly in.) After that, you can peel off the paper. (The transfer paper will peel off on its own, and removing photo paper requires placing it in a tray of hot water to soften it.) The transferred ink will become a resist to etching acid.

Close the edges of the steel product. You can stick duct tape on the edges of the steel or paint over them. Both methods prevent pickling of the edges of the steel product.

Choose the acid you will use to pickle the steel. Possible alternatives are hydrochloric (hydrochloric) acid (HCl), nitric acid (HNO3), or sulfuric acid (H2SO4). As pickling agents, certain substances can be used that are not acids, but give an acidic environment in water, such as iron (III) chloride (FeCl3) or copper sulfate (CuSO4). The strength of the acid determines the pickling rate of the steel. You can purchase etching acids and compounds from chemical or electronics supply stores.

• To make a hydrochloric acid solution, iron(III) chloride is usually mixed with water in equal amounts. It is most commonly used on copper, but works well on stainless steel as well. It is used in combination with a wider range of resist materials compared to other acids; however, without proper attention, it can cause surface pitting.
• Copper sulfate is more suitable for pickling mild and stainless steels. It is better to mix it with sodium chloride (NaCl - common table salt) in a ratio of 1 to 1 to prevent the formation of copper deposits on the surface of the steel, which will stop the pickling process. The blue solution gradually tarnishes as the etching process progresses and becomes colorless at the end of the etching process.
• Nitric acid is usually mixed in a ratio of 1 part nitric acid to 3 parts water. It can also be mixed with acetic acid (vinegar) in a ratio of 1 to 1, or with hydrochloric acid.
• Use sulfuric acid only with a concentration of 10 to 25 percent. A dilute sulfuric acid solution is generally more effective than a concentrated one. However, acids attack steel longer than compounds that form acids with water.

Immerse the steel product in a bath of pickling acid. Generally, the steel plate should be placed face down in the solution, so that the etched metal will flake down from the plate. This gives sharper lines when pickling steel. If you put the plate face up, then you can sweep away the flakes with a light brush or pen as they form, this will also remove the resulting bubbles. (Bubbles slow down the etching process, but if left they can form interesting patterns.) Leave the steel plate on until the lines are as deep as you want.

• Whether you put the steel plate face up or down, raise it in some way above the bottom of the tub. (This is especially important when the plate is face down.)
• Periodically shake the pickling bath to keep the solution well mixed.

The removal of part of the surface layer of a metal product by a chemical reaction is called etching. This technology has been known to man for several millennia, along with chasing and blackening, it was used to finish metal parts of weapons and household utensils, jewelry and ritual items. Nowadays, metal etching is used in art crafts, for electroplating, for creating images and inscriptions on metal products.

The essence of the method

Before etching, on those parts of the metal surface that should not be etched, a protective coating is applied that is resistant to the etching substance (mordant).

Next, the part is exposed to an acidic environment or immersed in a container with an electrolytic liquid. The longer the part is processed, the greater the layer of metal is corroded by the aggressive environment. Metal etching can be carried out in several stages, this is the so-called multilayer etching.

Etching of images on metal is carried out both in industrial and at home conditions.

Metal etching methods

Based on the materials used to corrode the metal layer, there are such methods of etching metals as:

• Chemical (liquid). Acid solutions are used. It does not require complex equipment and expensive materials. Vapors that are harmful to health are produced during operation.
• Electrochemical. An electrolyte solution is used and an electric current is passed through it. It is characterized by a higher speed of the process, more accurate execution of the details of the pattern, economical consumption of the working fluid. Does not produce harmful fumes
• Ion-plasma (dry). The surface layer is evaporated by an ionized plasma beam. Used in the production of microelectronic components.

The ion-plasma method requires high-precision and expensive equipment and is used only in industrial production. Liquid method, electrochemical metal etching and even electrochemical engraving are available at home.

With the help of galvanic etching, you can independently make a printed circuit board that is almost as good as an industrial one.

Metal galvanic etching

The galvanic etching method compares favorably with the liquid etching method because it does not require the use of acids that produce harmful fumes. Depending on the workpiece material, different electrolytic solutions are used:

• Steel and iron - ammonia and iron sulfate
• Copper and its alloys (bronze, brass) - copper sulfate
• Zinc - zinc sulfate.

To carry out the process at home, you will need:

• Electroplating bath made of non-conductive material.
• Power supply for 5 volts DC.
• Metal cathode (from the same metal as the workpiece.)
• Wire hangers for workpiece and cathode. The workpiece should not touch the walls or bottom of the tub.
• Two conductive rods longer than the tub.

One rod is connected to the negative terminal of the power supply and the cathode is hung on it.

The other rod is connected to the positive terminal and a product is hung on it, which will serve as the anode.

When voltage is applied, the process of electrolytic transfer of metal from the product to the cathode begins. It will occur from areas of the surface that are not covered with a protective varnish.

Artistic metal etching

Artistic etching of metal is carried out both by galvanic and liquid methods.

Masters of folk crafts and just home craftsmen receive with its help highly artistic images on cold steel and firearms, all kinds of forged and cast utensils. For craftsmen who make author's hunting and household knives, etching has become an almost indispensable element of decoration. Hunting scenes, Arabic, runic or abstract geometric ornaments are especially popular. Many craftsmen combine metal etching with bluing, giving the pattern a bluish, black or yellowish tint.

To transfer images, both the method of coating the part with varnish and glossy paper are used. Another method is also used - gluing the part with tape. The lines of the pattern are scratched with a hot needle, after which the adhesive tape is carefully removed from the areas to be etched with tweezers. The remains of the adhesive mass must be washed off with a solvent.

Before pickling, the part must be thoroughly degreased.

Metal surface preparation

Before etching, the surface must be prepared. This will ensure:

• High process speed
• removal of metal in an even layer.

During surface treatment, all mechanical and chemical contaminants are removed from it. A warm soapy solution is used for it, any detergent will do. After the surface has dried, it must be wiped with a rag soaked in a solvent or degreaser. This will remove residual liquid and oil films.

Chemical processing is well combined with mechanical:

• mirror polishing
• sanding. Used when polishing is not available. It should be ensured that the skin moves in the same direction all the time and the traces of it are strictly parallel.

Machining will significantly improve the appearance of the product after etching.

drawing

There are several methods for this operation. All of them are united by a common principle: protecting part of the surface from the corrosive action of the mordant, and distinguishes between the substance used to apply the pattern.

Nail polish

Popular and affordable way. Has some disadvantages:

• The high viscosity of the varnish makes it impossible to draw fine details and fine lines.
• Requires a steady hand and skill in drawing.
• It is very difficult to correct erroneously applied details.

Primer or bituminous varnish

The primer GF 021, XV 062 or bituminous varnish is used. First, the entire etched product is covered with the substance. Next, with a thin pen or marker, the contours of the drawing are transferred. From a thin wire or soft alloy rod, a needle should be made by sharpening the end of the wire.

Those areas of the image that should be etched are scratched to the metal. Care must be taken to ensure that the primer does not chip off.

Glossy paper

In addition to glossy paper (you can buy it at art supply stores, or you can simply cut out a sheet from a magazine), you will need a laser printer, an imaging application, and an iron. The image of the picture should be mirrored and printed in full size. The image is applied to the surface and ironed several times. After the workpiece has cooled, the paper is washed off with warm water, and the toner remains on the surface of the part. The back and side surfaces that are not subject to etching must be protected with varnish or plasticine.

The main advantage of the method is that you can accurately transfer the smallest details of the image.

The main disadvantage is that you can only work with flat or cylindrical workpieces in this way. The method is very popular in the manufacture of printed circuit boards.

Steel Pickling

In addition to artistic metal etching, which allows obtaining exquisite images on steel surfaces, steel etching is also used to remove scale and oxide films. In this case, it is necessary to carefully observe the requirements of the technological process in everything related to the concentration of pickling solutions and the exposure time of the part in the pickle or in the electrolyte bath. Overetching during such an operation is highly undesirable.

When pickling steel, both liquid and electrochemical methods are used. Pickling is prepared on the basis of strong acids, such as hydrochloric or sulfuric. Particular attention should be paid to thorough degreasing of the surface. A missed oil or grease stain can render the workpiece unusable. To protect parts of the workpiece that are not subject to etching, I use varnishes based on rosin, turpentine, and tar.

These components are highly flammable, so when working with varnish, you should be especially careful and careful. At the end of etching, the unetched parts of the workpiece are cleaned of the protective varnish with a solvent.

Picklings used for steel

Nitric acid is very popular among home craftsmen - picklers. It is used as the only basis for pickling, and mixed with tartar or salt. A metal pickling solution based on a mixture of nitric and hydrochloric acid is very reactive and should be handled with extreme care.

For the treatment of hard and special steel grades, mixtures of nitric and acetic acid are used. The processing is carried out in two stages. First, a special preliminary dressing is prepared - glyphogen, which is a mixture of water, nitric acid and ethyl alcohol. In it, the part is kept for several minutes. Next, the workpiece is washed with a solution of ethyl alcohol in distilled water and dried thoroughly. After that, the main etching is carried out.

Sulfuric acid solutions of medium concentrations are used for pickling cast irons.

Pickling of non-ferrous metals

Based on their atomic weight and the physicochemical properties of the substance determined by it, for each metal and alloy they select their own mordant that best affects it.

Both pure copper and copper alloys are pickled using sulfuric, hydrochloric, phosphoric, and nitric acid. Chromium or nitrogen compounds are added to the solutions to increase the reaction rate. At the first stage of etching, scale and oxide film are removed from the workpiece, then proceed to the actual etching of the metal. Care must be taken when pickling copper at home.

Aluminum and alloys based on it are distinguished from other metals by the fact that not acidic, but alkaline solutions are used for their etching. For molybdenum, alkaline solutions based on caustic soda and hydrogen peroxide are also used.

Titanium stands even more apart - at the first stage of preliminary pickling, alkali is used, and at the main stage, acid is already used. For titanium, I use the strongest acids - hydrofluoric and concentrated sulfuric and nitric. Titanium blanks are pickled to remove the surface layer of oxides immediately before being electroplated.

To pickle metals such as nickel or tungsten, an aqueous solution of hydrogen peroxide and formic acid is used.

PCB etching

The blank for the printed circuit board is a textolite sheet, coated on one or both sides with a layer of copper foil. The purpose of etching printed circuit boards is to create conductive traces of copper foil exactly according to the drawing. The tracks are covered with a protective varnish, the rest of the foil is removed by etching.

At home, it uses several methods:

1. Ferric chloride. The reagent is purchased at a chemical supply store or made independently. Iron filings should be dissolved in hydrochloric acid. Before use, the solution should be kept until the iron is completely dissolved and mixed thoroughly.
2. Nitric acid.
3. An aqueous solution of sulfuric acid mixed with hydrogen peroxide tablets.
4. Copper sulphate with the addition of hot water and sodium chloride. This option is the safest, but also the longest. Throughout the entire process, the temperature of the pickle must be maintained at least 40 ° C, otherwise the pickling will last for many hours.
5. electrolytic method. You should take a dielectric container (cuvettes for developing photographs are well suited), fill it with a solution of sodium chloride, place a board and a piece of copper foil there, which will serve as a cathode.

After etching with a liquid method, the board should be thoroughly rinsed with a solution of soda to extinguish the remaining acid.

Pickling process for other materials

In addition to metals, other materials are subjected to etching operations. Glass etching is most common for decorative purposes. Etching is carried out in vapors of hydrofluoric acid, the only one capable of dissolving glass. At the stages of preparation, a preliminary acid polishing of the surface of the product is carried out, then the contour of the future image is transferred to it. Protective coatings for glass are made from a mixture of wax, rosin and paraffins. After applying a protective coating, the workpiece is dipped into a pickling container.

The use of hydrofluoric acid creates a beautiful matt structure on the surface. To obtain a smooth, transparent surface, concentrated sulfuric acid is added to the pickling mixture. To obtain a relief, deep pattern, the operation is repeated.

Pickling Safety

In metal etching, extremely chemically active substances are used - strong acids, alkalis and their solutions. If handled incorrectly, they can cause serious bodily harm and significant property damage.

Therefore, when working with them, special precautions must be observed and the safety rules must be strictly observed during work:

• Work is carried out only in the presence of good ventilation, preferably a fume hood.
• It is mandatory to use personal protective equipment: rubber gloves and an apron, thick industrial clothing, a respirator, a protective face shield.
• Do not place jars with acids and alkalis on high shelves and cabinets.
• During the dilution of acids, ACID is poured into WATER, and never - water into acid.
• When working with an acid, have a soda solution on hand, and when working with an alkali, a weak acetic solution to wash areas of the skin that accidentally got drops of the solution.
• When working with the galvanic method, before starting work, carefully inspect all used electrical equipment for the absence of mechanical damage and the integrity of the insulation.
• Have a proper fire extinguisher handy.

In case of skin contact with pickling solution, immediately wash the affected area with an appropriate neutralizing solution. If acid or alkali splashes on clothing, it should be removed immediately.

If the pickling solution gets on the mucous membranes, you should immediately seek medical help. Delay in such cases can cost health or even life.