Fake NO.4 finishes flood the market, costing buyers thousands in failed projects. Learn the professional techniques to spot genuine finishes before you pay.

Authentic NO.4 finish shows uniform directional polishing lines at 150-180 grit, consistent reflectivity (not mirror-like), and proper RA surface roughness (0.3-0.5μm) - fakes often have uneven patterns, wrong gloss levels, or hidden coating.

After catching multiple counterfeit shipments for clients, I've developed these foolproof verification methods. Let me show you how to protect your purchases.

What is a number 4 steel finish?

Many buyers confuse NO.4 with other finishes, leading to wrong material selection. Understanding its true characteristics prevents costly mistakes.

NO.4 finish¹ is a brushed stainless steel² surface with consistent directional polishing lines, created using 150-180 grit abrasives - it offers semi-reflective appearance, good corrosion resistance, and hides fingerprints better than mirror finishes.

Key Identification Features

1. Visual Characteristics

   • Proper appearance:	Feature	Authentic NO.4
     Reflectivity	30-40%
     Line Pattern	Unidirectional
     Texture Depth	Visible

2. Technical Specifications

   • Surface roughness:
     • RA: 0.3-0.5μm
     • Rz: 3-5μm
   • Grit size standards:
     • Initial grinding: 120-150
     • Final polishing: 180-220

3. Common Fakes to Spot

   • Coated finishes:
     • Peels under scratch test
     • Uneven weathering
   • Improper polishing:
     • Cross-grain patterns
     • Over-polished areas

A hotel in Qatar received "NO.4" sheets that showed patchy discoloration after 6 months. Testing revealed they were actually coated 2B sheets with fake brushing - a $80,000 mistake.

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How to identify real steel?

Counterfeit steel products have become sophisticated. These professional verification methods separate genuine stainless from fakes.

Real stainless steel shows non-magnetic properties (304/316), consistent 7.9g/cm³ density, and passes acid tests (16% nitric acid shows no reaction) - fakes often fail these basic checks or show inconsistent material properties.

Verification Techniques

1. Physical Tests	Test	Real Steel Result	Fake Result
   Magnet Test	Slightly magnetic	Strongly magnetic
   Spark Test	Short orange	Long yellow
   Density Check	7.9g/cm³	Varies

2. Chemical Analysis

   • Spot test kit results:	Grade	Ni%	Cr%	Mo%
     304	8-10	18-20	-
     316	10-14	16-18	2-3

3. Surface Examination

   • Authentic features:
     • Uniform grain structure
     • No coating layers
     • Consistent polishing marks
   • Fake indicators:
     • Paint-like surface
     • Peeling edges
     • Color variations

A contractor in Thailand avoided $50,000 in fake steel by using simple acid tests on samples. The "316" material bubbled immediately, revealing carbon steel underneath.

How to identify steel grade?

Wrong grade identification causes catastrophic failures. These professional methods ensure you get exactly what you specify.

Use XRF analyzers¹ for instant grade verification (shows Cr/Ni/Mo content), check mill test certificates² against EN/ASME standards, and perform PMI tests - visual identification alone is unreliable for grade confirmation.

Grade Verification Methods

1. Instrument Testing

   • XRF gun capabilities:	Element	Detection Range
     Chromium	13-30%
     Nickel	0-50%
     Molybdenum	0-10%

2. Document Verification

   • Certificate checks:	Document	Key Verification Points
     MTC	Heat number, grade stamp
     EN 10204 3.1	Independent lab sign
     ASTM A480	Chemistry ranges

3. Mechanical Testing

   • Grade-specific properties:	Grade	YS (MPa)	TS (MPa)	Elongation
     304	205	515	40%
     316	205	515	40%
     430	310	450	20%

A chemical plant in Malaysia discovered their "316L" pipes were actually 304 after PMI testing. The missing molybdenum would have caused catastrophic failure in chloride service.

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How to tell if stainless steel is coated or not?

Coated fakes compromise corrosion resistance¹. Learn these professional techniques to detect hidden coatings.

Authentic stainless steel shows uniform metal composition throughout (check cut edges), passes 100-hour salt spray tests, and maintains consistent surface under acid etching - coatings peel, bubble, or discolor under these tests.

Coating Detection Methods

1. Visual Inspection

   • Coating indicators:	Location	Signs of Coating
     Cut edges	Color difference
     Bent areas	Cracking/flaking
     Welds	Discoloration

2. Chemical Tests

   • Acetone rub test:
     • Coated: Color transfers
     • Real: No change
   • Nitric acid test:
     • Coated: Bubbles/peels
     • Real: No reaction

3. Performance Testing

   • Salt spray results:	Material	100-hour Result
     Real 316	No rust
     Coated steel	Edge rusting
     304	Surface staining

A Dubai skyscraper facade failed when "316" sheets rusted after one season. Investigation revealed carbon steel with thin chrome plating - a $2 million lesson in verification.

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Conclusion

Proper identification prevents costly material mistakes - never trust appearances alone with stainless steel.