How Is Mirror Finish Stainless Steel Made? How to Judge the Polishing Grade?

Mirror finish stainless steel is a high-gloss stainless steel sheet that is polished to a smooth, reflective surface, much like a mirror. Due to its sleek, modern appearance and excellent corrosion resistance, it is widely used in elevator interiors, feature walls, building facades, hotel lobbies, and decorative applications.

But how exactly is a mirror finish stainless steel sheet produced? And how can we distinguish between different polishing grades like 6K, 8K, and 10K?

This article provides a comprehensive look into the complete manufacturing process of mirror stainless steel—from raw material selection to final 8K polishing—and offers clear, practical guidance on how to evaluate the polishing quality.

1. The Complete Manufacturing Process of Mirror Finish Stainless Steel

Although polishing is the key step, creating a flawless mirror finish requires careful control throughout the entire production process.

Step 1: Raw Material Selection (Base Material)

The process starts with selecting high-quality cold-rolled stainless steel coils. Commonly used grades include:

• 201: Economical, high hardness, good for decorative purposes (indoor use);

• 304: Widely used, excellent corrosion resistance for both indoor and outdoor applications;

• 316: Premium grade for medical, coastal, or high-humidity environments.

The surface should be flat, clean, and free from oxidation, pits, or scratches to ensure even polishing.

Step 2: Annealing and Surface Preparation

Cold-rolled coils are softened through bright annealing to prepare the surface for polishing. There are two types:

• 2B finish: Dull, needs multiple sanding stages;

• BA finish: Naturally shiny, easier to polish to a mirror finish.

Step 3: Surface Sanding and Pre-Polishing

This step removes surface imperfections and creates a uniform base:

• Rough sanding: Using 120#–400# abrasives to flatten and clean the surface;

• Intermediate sanding: Using 600#–800# belts for smoother finishes;

• Fine sanding: Over 1200# grit to prepare for final mirror polishing.

Operator experience and equipment quality greatly influence the outcome here.

Step 4: Mirror Polishing (8K Processing)

This is the core step, where polishing machines equipped with cloth wheels and polishing compounds (like chromium oxide or alumina) are used to create the 8K mirror surface.

• Each sheet is polished several times;

• The process takes 15–30 minutes per sheet;

• Advanced finishes like 10K require ultra-fine polishing.

Step 5: Cleaning and Degreasing

After polishing, the surface is covered with oil and residues. Specialized ultrasonic cleaning removes all contaminants, ensuring a flawless shine.

Step 6: Protective Film Application

The final step is applying PE film to protect the mirror surface from scratches during transport or processing. Options include:

• Laser film (for laser cutting);

• White/black PE film (for general protection);

• Blue film (easy to identify and peel).

2. How to Judge the Polishing Grade of Mirror Stainless Steel?

Terms like 6K, 8K, or 10K are commonly used in the industry, but what do they really mean? Here are 5 key methods to assess the polishing level of a mirror finish stainless steel sheet:

1. Glossiness (GU – Gloss Units)

Use a gloss meter at a 60° angle to measure surface reflectivity:

2. Image Clarity

Stand 1.5 meters away from the sheet and look at your reflection:

• A high-grade mirror finish will show clear, sharp outlines;

• Lower grades will look blurry or distorted.

This is a simple and effective way to judge quality visually.

3. Surface Defects

Inspect the sheet for any visible flaws:

• Scratches, waves, pinholes, or uneven brightness indicate poor polishing;

• Shine a flashlight at different angles to check for micro-scratches.

4. Surface Roughness (Ra Value)

This is a technical measurement of surface smoothness. The lower the Ra, the smoother the finish:

Finish Level	Roughness (Ra μm)
Basic Mirror	0.2–0.1
8K Mirror	≤ 0.05
10K Mirror	≤ 0.02

Industrial or precision applications may require certification of Ra values.

 

5. Reflection Uniformity

Place two sheets side by side and observe:

• Is the reflection color consistent?

• Are reflections straight or warped?

• Is the finish equally bright across the surface?

Uniformity is crucial, especially for large installations or cladding.

3. Application Scenarios & Grade Suggestions

Here’s how to choose the right mirror finish level depending on your application:

Conclusion: Know the Process, Recognize the Quality

Understanding how mirror finish stainless steel is produced—along with how to evaluate its quality—gives buyers a major advantage. Whether you are sourcing for a high-end interior design project or a commercial architectural façade, choosing the right grade and finish will directly affect the final look and longevity of your design.