The formation principle of brass color: Analysis of the color change mechanism behind it

Brass, an ancient and ever-new alloy material, is widely used in construction, decoration, jewelry and other fields with its unique color and excellent mechanical properties.

The change of brass color is not only closely related to its composition, but also affected by various factors such as environment, oxidation, corrosion, etc., and the color of brass can also be changed by coloring. This article will focus on the relevant content of brass color to explore its formation principle and the color change mechanism behind it.

1.Basic composition and brass color

Brass is an alloy composed of two metal elements, copper (Cu) and zinc (Zn). Copper itself has an orange-red color, while zinc is silvery white. When these two metals are mixed in different proportions, a series of brass materials with different colors are formed. As the zinc content increases, the color of brass gradually changes from red to golden yellow. When the zinc content reaches a certain proportion, brass presents a bright golden yellow, which is also the most common appearance of brass.

(1) The alloy ratio of copper and zinc

The ratio of copper and zinc is the key factor affecting the color of brass. When the copper content is high, the color of brass tends to be more golden or dark yellow, because the metallic luster of copper dominates the alloy. Generally speaking, if the copper content is greater than 60%, the color is relatively yellow, and some are more common, such as H65, H68, H70, etc.

On the contrary, when the zinc content increases, the brass color becomes lighter and tends to pale yellow or yellowish-white, because the silvery-white luster of the zinc begins to influence the overall tone of the alloy. The different alloy proportions not only affect the color of brass, but also determine its mechanical properties such as hardness, strength and corrosion resistance.

(2) Surface oxidation and color change

When brass is exposed to air, it reacts with oxygen to form an oxide film. This oxide film is mainly composed of cuprous oxide (Cu2O) and cupric oxide (CuO). Cuprous oxide is rose red, while cupric oxide is black. The thickness and composition of the surface oxide film determine the change in the color of the brass surface, which gradually changes from the initial orange-red to brown or brown.

This oxidation reaction not only affects the appearance of brass, but also improves its corrosion resistance. In some decorations and applications, people deliberately use chemical methods to accelerate the oxidation process of brass to achieve a specific color effect. For example, many antiques and decorations use the natural oxidation characteristics of brass to create a retro effect.

2.Environmental factors affecting brass color

Brass color is not only affected by its composition and surface oxidation, but also related to a variety of factors in the environment. Humid environment, acidic medium, oxidizing agent, etc. will accelerate the oxidation and corrosion of brass, leading to the change of its surface color.

(1) Humid environment

Brass is prone to corrosion in a humid environment because moisture promotes electrochemical reactions on the surface of brass and generates various corrosion products, such as sulfates and nitrates. These corrosion products not only change the color of brass, but may also affect its mechanical properties. Therefore, keeping brass products dry is an important measure to prevent them from discoloring.

(2) Acidic medium

Acidic media such as acid rain, acidic soil and certain acidic chemical products will accelerate the corrosion process of brass. When brass comes into contact with an acidic medium, the acidic substance will react chemically with the brass surface to generate corrosion products, causing the brass surface to darken in color. Common corrosion products include basic copper carbonate (Cu₂(OH)₂CO₃) and basic copper sulfate (CuSO₄·3Cu(OH)₂), which are usually blue-green and commonly known as “patina”.

(3) Oxidants

Certain chemicals such as hydrogen peroxide and nitrous oxide have the ability to oxidize brass. These oxidants react with the brass surface to generate substances such as copper oxide, causing the color of brass to change. In order to prevent the oxidant from damaging the brass, an appropriate protective agent can be applied to the brass surface to form a protective film to reduce the contact of brass with the external environment.

3.Brass coloring methods and techniques

(1) Chemical coloring method

Chemical coloring is the process of generating a colored film on the brass surface through a chemical reaction. This is usually achieved by immersing the brass in a solution containing specific chemicals, such as sulfides, oxides or other salts.

These chemicals react with the copper and zinc on the brass surface to form a film of compounds of different colors. By controlling the composition of the chemical solution and the reaction time, the brass color can be precisely regulated to achieve a golden yellow surface or other color requirements.

(2) Electrochemical coloring

Electrochemical coloring is a technology that forms a colored film on the surface of brass through an electrolytic process. In this method, brass is used as an anode and immersed in an electrolyte containing metal salts.

When an electric current passes through, the metal ions on the surface of the brass react with the ions in the electrolyte to form an oxide film of various colors. The advantage of electrochemical coloring is that the thickness and color of the film layer can be precisely controlled, and the color is uniform and long-lasting.

(3) Other coloring techniques (such as heat treatment and coating)

In addition to chemical and electrochemical coloring, brass can also be changed in color through heat treatment and coating. Heat treatment is to change the color of brass by forming different oxide layers on the surface of brass through controlled heating and cooling processes.

Coating is to change the color by applying a layer of paint or metal film on the surface of brass, such as spraying or electroplating. These methods can be selected and used according to specific application requirements.

4.Maintenance and care of brass color

(1) Daily cleaning and maintenance

In order to maintain the luster and golden color of brass, regular cleaning is necessary. In daily maintenance, you can use a mild detergent and a soft cloth to wipe it, and avoid using strong acid or strong alkaline detergents. These chemicals may damage the oxide layer on the surface of brass.

(2) Anti-oxidation treatment technology

In order to prevent brass from oxidizing, a transparent protective film such as varnish or resin can be coated on its surface. These coatings can isolate air and moisture and reduce the occurrence of oxidation reactions. In addition, chemical methods can also be used, such as forming a stable oxide film on the surface of brass to improve its antioxidant capacity.

(3) Repair and renovation technology

For brass products that have been oxidized or damaged, they can be repaired by chemical or mechanical methods. Chemical repair usually involves using a specific chemical solution to remove surface oxides and restore the original luster of brass. Mechanical repair may include steps such as grinding and polishing to remove surface damage and oxide layers.

5.Importance of brass color in various fields

(1) Decorative art field

Brass color is favored for its warm and retro texture. It is often used to make various decorations such as lamps, photo frames, ornaments, etc., which can add elegance and luxury to the home environment.

In architectural decoration, brass is widely used in door handles, railings, sculptures and other parts. Its unique color can enhance the overall beauty and grade of the building.

(2) Fashion accessories field

Brass color has always maintained a high popularity in the fashion industry. Designers often use it to make accessories such as belt buckles, watches, bracelets, necklaces, etc. The color of brass can highlight the wearer’s taste and personality.

With the popularity of retro style, brass-colored accessories such as eyeglass frames and bags have also become a must-have item for fashion gurus.

(3) Industrial design field

In industrial design, brass color is often used to make the appearance of high-end electronic products, such as speakers and headphones. Its color can convey the high-end quality and exquisite craftsmanship of the product.

Brass has good mechanical properties and corrosion resistance, so it is often used in key components of some industrial equipment and devices, and its original color is maintained to demonstrate its reliability and professionalism.

(4) Musical instruments antiques

Some musical instruments, such as copper instrument parts and pipe bodies of wind instruments, are often made of brass alloys. Brass has a unique timbre and can add rich sound effects to musical instruments.

Due to its appearance, brass is also widely used in the field of antique restoration and imitation. It is often used to make antique parts or repair antique furniture to extend the vitality of historical relics.

6.Summary

By understanding the formation principle and mechanism of brass color, we can better protect and utilize this ancient and ever-new material. Whether it is the unique color formed by natural oxidation or the artificial color obtained by chemical coloring process, brass plays an important role in various fields with its rich colors and excellent mechanical properties. In the future, the application fields of brass will be more extensive, and the mystery of brass color change will continue to attract people to explore and research.