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what is bronze made of ?

April 07, 202123

Bronze is an alloy in which tin or lead is added to pure copper (red copper).


Bronze is the earliest alloy in the history of metal smelting and casting. The addition of tin or lead to pure copper (red copper) has special importance and historical significance. Compared with pure copper (red copper), bronze has high strength and low melting point (25%). For bronze smelted with tin, the melting point will drop to 800°C. The melting point of pure copper (red copper) is 1083°C). Bronze has good castability, wear resistance, and stable chemical properties.


Bronze has the characteristics of low melting point, high hardness, strong plasticity, wear resistance, corrosion resistance, and bright color. It is suitable for casting various appliances, mechanical parts, bearings, gears, etc.

A perfect bronze ware, its shape, decoration, copper quality, cast marks, rust color, especially the charm, must be the same as the original antiquities. The production process is divided into two processes: the production of copper tires and the overall old treatment.

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1. Copper tire production process:

(1) Master mold making: a good bronze ware must have a perfect master mold. This is the most critical step in the production of bronze ware. If it is a copy, you need to clean the ancient artifacts with a professional bronze rust removal method and then remake the mold; if it is a copy, you need to carve a mother model that is the same as the original ancient artifact. The method of making the master model is: according to the picture or the original antiquities, use paraffin wax or treated plaster to shape the shape similar to the ancient artifacts. Whether the shape of the ancient artifacts is accurately shaped, you can modify it when you further engrave the decoration and shape it according to the picture. , When carving, due to poor vision, it is impossible to determine the specific location and size of the original decoration. We use the symmetrical midline of the ancient artifact as a starting point, and calculate the position and size of the coarse flower and the fringe according to the size of the ancient artifact and the size of the photo. Then carve the pattern on the molded vessel. When there is a difference, adjust the shape of the molded vessel until the pattern is evenly distributed on the surface of the vessel. When carving patterns, the pattern base must be flat, the lines must be smooth, and the depth of the pattern carving must be consistent with the original antiquities. According to this method, if the patterns on the ancient artifacts can be evenly engraved on the already molded shapes, the production of the master mold is basically completed. Problems that easily occur in the process of master mold making: using mold wax as the material is prone to burrs and round sun patterns. In ancient times, patterns were carved on the clay fan, and the surface of the sun pattern was flat and square.

(2) Remanufacturing molds: In the past, plaster was used to remake molds. After the plaster is solidified, the texture is brittle and loose. Therefore, the texture of the mold is not strong, the lines are not smooth, and the utilization rate is not high. Deformed and lose the charm of the original antiquities. Nowadays, mold remaking generally uses greenhouse vulcanized silicone rubber. Not only is the method simple, but the mold produced is very effective. Especially the molds reproduced on the original antiquities can reproduce the shape, pattern and charm of the original antiquities without losing their shape. The disadvantage of this method is that the whole shape is slightly shrunk than the original antiquities, but the proportion is small. If it is not compared with the original antiquities, it is difficult to distinguish the shrinking feeling with the naked eye.

(3) Mold shell production and casting polishing: Lost wax casting is generally used nowadays, this method is simple and quick, and can not lose the charm of the original shape, and can be cast into particularly complex bronzes. The disadvantage is that the wall thickness of the tyre is uneven. Use a silicone rubber mold to pour out the lost wax mold shell, which must be trimmed internally and externally. The outer surface of the wax shell should be smooth and not deformed; the inner correction should be made to make the thickness uniform, sharp edges and corners, smooth and flat. Bottom line and gasket production specifications. The casting adopts the precision casting method, which will not be described in detail here. The cast objects must be finely polished and polished. When polishing, we must protect the original shape and pattern of the copper tire, and try our best to make the pattern clear and natural, exquisite and smooth.

2. The old copper tires (black paint ancient leather shell, erythema, green rust old method): Only a perfect copper tire without a beautiful coat, can not be regarded as an exquisite reproduction. The old methods in the past can no longer meet people's appreciative requirements. Now, the old methods use a comprehensive method of electrolytic skinning, chemical rusting, and new treatment of sticky rust. The following is only a detailed introduction to the old methods of black lacquer, erythema, and green rust.

(1) Electrolysis method to make leather case: The required instruments include a regulated DC power supply, a water bath heating pot, and a heating electric furnace. Suspend the old bronze ware into the water bath heating pot, then pour the soil with the chemicals into the pot, and bury the bronze ware in it. The bronze is connected with the positive pole of the stabilized power supply with a wire, and the negative pole of the stabilized power supply is connected with the shell of the water bath. The bottom of the water bath is heated by an electric furnace, and the temperature is maintained at about 90°C. Chemical formula: 100 grams of potassium dichromate, 100 grams of copper sulfate, 50 grams of acetic acid, 50 grams of hydrogen peroxide, appropriate amount of distilled water, and appropriate amount of loess. After mixing the chemicals, distilled water, and loess evenly, put them into the heating barrel, turn on the power, connect the negative pole to the heating barrel, and connect the positive pole to the copperware. The current is controlled at 0.1mA~0.3mA, the voltage is controlled at 1V~2V, and the heating temperature is around 90℃. After about 10 days, a layer of black paint is formed inside the surface of the bronze. Turn off the power and take out the bronze to clean it up.

(2) Red spots and colorful cloud-like green rust spots on the surface of the black skin. Production method: use 100 grams of copper acetate, 100 grams of copper nitrate, 100 grams of ammonium carbonate, 150 grams of basic copper carbonate, 50 grams of ammonium chloride, appropriate amount of distilled water, operation method Same as above. The current is 0.5mA, the voltage is 1V, and the time is about 20 days. On the surface of the bronze ware, dot-shaped and flake-shaped erythema and colorful cloud-shaped green skin can be formed.

(3) Green rust production method: Before rusting, cover the black skin, erythema, and green skin that need to be preserved with silicone rubber to prevent further chemical reactions from destroying the original skin. Chemical reagent formula: 200 grams of ammonium carbonate, 500 grams of ammonium bicarbonate, 100 grams of hydrochloric acid, 100 grams of ammonia, specific operation method: dissolve ammonium carbonate, ammonium bicarbonate, and hydrochloric acid in a porcelain container, together with the ammonia that opened the cap Put it into a high-pressure tank, and suspend the bronze in the high-pressure tank, then seal the high-pressure tank and heat it at the bottom to keep the tank at 2 to 3 atmospheres. Change the chemical reagents every month. After 3 to 5 months, flakes or dots of green rust will be formed on the surface of the bronze, and some parts still have crystal rust. The disadvantages are: the color tone is single, and the layering of rust is not strong.

(4) Manual processing method: Generally, the rust flakes on ancient copperware with rich rust color and strong layering are separated from the copper tire by ultrasonic vibration, and these rust flakes are transplanted to different parts of the replica, and then used High-grade white cement is added with ore color to reconcile different rust colors. According to the rust color level and shape of ancient copperware, at the interface of the replica mosaic piece or where the rust color is lacking, a variety of layering feelings and vivid colors can be made Rusty. Wrap the processed copperware with a damp cloth, put it in the steamer and steam for 3 to 5 hours, and then take it out to dry. Because it is chemically made rust, the copperware smells not earthy, but slightly sour. You need to take an appropriate amount of fresh grave soil to make a paste with water, put the replica in it for about 10 days, and take it out and clean it up. The new imitation bronze ware has an earthy fragrance, like ancient bronze ware. It is difficult to distinguish the authenticity of the high-end replicas produced by the above methods without cutting the copper tires to see the copper quality. The reason is: the copper has been destroyed, the hand feels very light, the rust color is rich in layers, it is not afraid of boiling in water, and the rust color can react with acid, just like real rust. The disadvantages are: the damaged copper tire is not earthy red, but grayish white, and it is loose and not hard. The rusty copper tires of the original bronzes are hard and dense earth red.

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