When processing metals, it is not uncommon to see a multi-colored hue appear on the surface, ranging from light yellow to blue-violet. This effect is called tarnishing of metal and occurs on both steel and stainless steel. For industry and metalworking, this phenomenon is important to understand, as it affects the aesthetics, strength, and quality of parts.

In this article we will take a detailed look at What is metal tarnish, what causes it, and how can it be treated?, as well as methods of elimination and prevention.

🔧 What is metal tarnish?

Runaway - is a change in the color of the metal caused by surface oxidation when exposed to high temperatures.
A thin oxide film forms on the surface of the metal, which refracts light, creating characteristic colors: yellow, red, blue, violet.

The main manifestations of tarnishing:

Yellow and golden shades (up to 250 °C);
Red-brown (250–300 °C);
Blue and violet (300–400 °C);
Dark grey and black (>400°C).

⚙️ Causes of discoloration

Tarnishing of metal occurs due to thermal oxidationThe most common reasons are:

High temperature during heat treatment
- Hardening, tempering, welding, soldering and laser cutting often cause tempering.
Contact with oxygen
- Oxidation is enhanced by prolonged heating in air.
Chemical reactions
- Residues of oils, greases or acids on the metal surface may accelerate discoloration.
Incorrect cooling medium
- Rapid cooling with water or air sometimes results in uneven tempering.

🌈 How to determine tarnish

The color of the tarnish helps to estimate the temperature at which the metal was:

Color	Temperature, °C	Application
Light yellow	200–250	Light heat treatment
Yellow-brown	250–300	Beginning of the oxide layer
Red-brown	300–320	Medium heat
Blue and purple	320–400	High heat, requires removal
Gray/black	>400	Overheating of metal

💡 Important: Severe tempering may indicate overheating of the part and a decrease in the strength of the metal.

🧩 Methods for eliminating tarnish

There are several ways to remove tarnish and restore the metal to its original appearance:

Mechanical cleaning
- Grinding, sandblasting, polishing.
- Used for exterior surfaces and decorative items.
Chemical cleaning
- Acid solutions (hydrochloric, phosphoric) dissolve the oxide layer.
- Suitable for pipes, sheet metal and complex shaped parts.
Heat treatment
- Neutralization of tempering during hardening and tempering at the correct temperature.
- Restores the metal structure and reduces internal stress.
Passivation and coatings
- Application of corrosion inhibitors, anti-corrosion coatings or a stainless layer.
- Prevents recurrence of discoloration.

⚙️ Preventing fading

To reduce the risk of tarnishing on metal, it is recommended:

Use clean tools and lubricants during heat treatment;
Control heating temperature details;
Apply protective gas environments (argon, nitrogen) in welding and laser cutting;
Produce proper cooling parts after processing;
Apply protective coatings on sensitive parts.

🏭 The practical significance of tarnishing

On aesthetic products (decorative details, cases, facade elements) tarnishing is undesirable and requires removal.
IN technical structures Severe tarnishing may indicate overheating and a decrease in mechanical properties.
IN stainless steel A thin tarnish can serve as an indicator of processing temperature without compromising strength, but is often removed for aesthetics.

✅ Conclusion

Tarnishing of metal This is a natural phenomenon during heating, caused by the oxide film on the surface. The color of the tarnish helps determine the degree of heating and possible overheating.

To eliminate tarnish, mechanical, chemical, or thermal treatments, as well as protective coatings, are used. Prevention involves temperature control, surface cleanliness, and proper treatment.

Company Art-Metal offers manufacturing and processing of metal structures, including tarnish removal, polishing, and surface protection. We guarantee the quality, durability, and attractive appearance of our products.

📞 Contact the specialists Art-Metalso that the metal of your products is not only durable, but also aesthetically flawless.