Mirror Finish vs No.4 Finish

Which Stainless Steel Surface Is Right for Your Industry?

Choosing the right stainless steel surface finish is just as important as selecting the correct material grade.

Whether you process 304, 316L, 2205 Duplex, or other stainless steel alloys, the surface finish directly affects product appearance, corrosion resistance, cleanability, maintenance costs, and even production efficiency.

Among all industrial finishes, Mirror Finish and No.4 Finish are the two most commonly specified.

Although they are both produced by grinding and polishing, they are designed for very different applications.

In this guide, we compare their characteristics, manufacturing processes, advantages, and ideal applications to help manufacturers make the right decision.

What Is a Mirror Finish?

Mirror Finish (also called No.8 Mirror Finish) is a highly polished surface capable of producing clear reflections.

Industrial mirror polishing normally consists of multiple grinding and polishing stages until surface roughness reaches extremely low values.

Typical specifications include:

• Surface Roughness: Ra ≤ 0.02 μm

• Gloss: 600–700+ GU

• Nearly distortion-free reflection

• Extremely smooth surface

Because the surface contains almost no microscopic grooves, it offers excellent cleanability and corrosion resistance.

What Is a No.4 Finish?

No.4 Finish is produced by abrasive belt grinding.

Instead of reflecting light like a mirror, it creates a uniform linear grain.

Typical characteristics include:

• Straight brushed texture

• Soft metallic appearance

• Low reflection

• Excellent scratch resistance

• Easy maintenance

Rather than hiding scratches completely, No.4 Finish makes minor scratches much less noticeable during daily use.

Mirror Finish vs No.4 Finish

Manufacturing Process Comparison

Mirror Finish

Typical process:

Surface Inspection

↓

Rough Grinding

↓

Intermediate Grinding

↓

Fine Grinding

↓

Mirror Polishing

↓

Cleaning

↓

Drying

↓

Protective Film

Each polishing stage removes scratches left by the previous stage.

Any vibration, unstable pressure, or abrasive inconsistency may become visible in the final mirror surface.

No.4 Finish

The production process is simpler.

Surface Inspection

↓

Rough Grinding

↓

Intermediate Grinding

↓

Final No.4 Brushing

↓

Inspection

↓

Protective Film

Although fewer polishing stages are required, maintaining a perfectly uniform grain across large heavy plates still demands stable grinding pressure and precise machine control.

Which Industries Prefer Mirror Finish?

Mirror polishing is widely used where cleanliness and corrosion resistance are essential.

Typical industries include:

Chemical Processing

Reaction vessels

Pressure tanks

Heat exchangers

Pharmaceutical

Bioreactors

Sterile vessels

Mixing tanks

Food Processing

Dairy equipment

Brewing systems

Sanitary tanks

LNG & Energy

Cryogenic equipment

Pressure vessels

Hydrogen storage

Semiconductor

Vacuum chambers

Copper foil production equipment

Precision process systems

Which Industries Prefer No.4 Finish?

No.4 Finish is commonly selected where durability and appearance must be balanced.

Applications include:

• Elevator panels

• Building facades

• Kitchen equipment

• Architectural decoration

• Commercial furniture

• Industrial machinery

• Transportation equipment

Because the brushed grain hides daily wear better than mirror surfaces, it is ideal for high-contact environments.

Which Finish Is Easier to Maintain?

Both finishes are easy to clean.

However, their maintenance characteristics differ.

Mirror Finish:

Advantages

✓ Extremely hygienic

✓ Smoothest surface

✓ Lowest contamination

Disadvantages

× Fingerprints are more visible

× Surface scratches are easier to notice

No.4 Finish

Advantages

✓ Better scratch resistance

✓ Fingerprints less noticeable

✓ Lower maintenance frequency

Disadvantages

× Linear grain may trap contaminants if poorly finished

Therefore, surface quality—not simply the finish type—is critical.

Why Machine Quality Matters

Whether producing Mirror Finish or No.4 Finish, surface consistency depends heavily on equipment performance.

Key factors include:

• High-rigidity machine frame

• Precision contact rollers

• Constant grinding pressure

• Stable abrasive belt tracking

• PLC automation

• Accurate feed speed control

Even the best abrasive belts cannot compensate for poor machine stability.

LEBON MACHINERY Solutions

LEBON MACHINERY provides complete surface finishing solutions for:

• Mirror Finish

• No.4 Finish

• Hairline Finish

• Scotch-Brite Finish

• Anti-Fingerprint (AFP)

Our heavy-duty grinding and polishing systems process hot rolled stainless steel plates from 5 mm to 100 mm, helping customers produce premium surfaces for industrial and decorative applications.

Unlike many equipment manufacturers, LEBON also operates its own production lines, allowing continuous equipment optimization based on real manufacturing experience.

Frequently Asked Questions

Is Mirror Finish always better than No.4?

No.

The best finish depends on the application.

Mirror Finish is ideal for hygienic environments, while No.4 Finish is often preferred where scratch resistance and everyday durability are more important.

Can heavy plates achieve both finishes?

Yes.

Modern grinding and polishing systems can produce both premium No.4 and Mirror finishes on hot rolled stainless steel plates.

Which finish costs more?

Mirror Finish generally requires more polishing stages, longer production time, and tighter process control, making it more expensive.

Which finish does LEBON MACHINERY recommend?

We recommend selecting the finish according to your product application, material grade, customer requirements, and production objectives. Our engineering team provides complete process recommendations rather than simply supplying equipment.

Conclusion

Mirror Finish and No.4 Finish each offer unique advantages.

Mirror polishing delivers exceptional cleanliness, corrosion resistance, and visual quality, making it ideal for chemical, pharmaceutical, food, semiconductor, and energy industries.

No.4 Finish provides a durable, attractive brushed appearance that is widely used in elevators, architecture, commercial kitchens, and industrial equipment.

At LEBON MACHINERY, we help manufacturers produce both finishes with stable quality through advanced grinding technology, precision engineering, and years of practical production experience.

Whether your project requires a flawless mirror surface or a premium No.4 brushed finish, our complete surface finishing solutions are designed to maximize quality, efficiency, and long-term reliability.

CTA

Not Sure Which Surface Finish Is Right for Your Project?

Contact LEBON MACHINERY today. Our engineering team will recommend the most suitable grinding and polishing solution based on your material, thickness, production capacity, and target surface finish.