How can stainless steel be coloured, and what processes are available?

The term “stainless steel colouring” refers to processes that modify the surface appearance of corrosion-resistant steels. Unlike organic coatings such as paint or powder coatings, which form an opaque layer, professional colouring preserves the metallic structure and lustre of the substrate. For this purpose, mirrorINOX uses PVD/TiN coating and nanoINOX® technology. These methods either alter the refraction of light at the surface or apply ultra-thin, transparent to semi-transparent layers. The aim is to achieve a durable, UV-resistant and mechanically robust colour finish that meets the stringent requirements of B2B applications and exterior architecture.

Terminology and synonyms – relevant standards and names

In stainless steel processing, various terms are often used synonymously, although technically they define specific material groups.

V2A and V4A

These historical designations originate from Krupp’s test series 2 (austenite) and 4 (austenite), respectively. V2A (usually grade 1.4301) is the standard stainless steel for general applications. V4A (usually grade 1.4404) contains added molybdenum and offers greater resistance to chloride-induced corrosion, which is crucial when colouring stainless steel for projects in coastal areas.

AISI Standards

The American Iron and Steel Institute classifies stainless steel using three-digit numbers. AISI 304 largely corresponds to the European grade 1.4301, while AISI 316L corresponds to grade 1.4404. This nomenclature is particularly relevant for international tenders in façade construction and product design.

DIN EN 10088

This is the key European standard specifying the technical delivery conditions for stainless steels. It defines the chemical composition and mechanical properties that form the basis for every colouring process at mirrorINOX.

Chemical Composition

Suitability for colouring and subsequent corrosion resistance depend directly on the alloy. Stainless steel consists primarily of:

• Iron (Fe) as the base element
• Chromium (Cr): at least 10.5%, forms the protective passive layer
• Nickel (Ni): stabilizes the austenitic microstructure and improves formability
• Molybdenum (Mo): increases resistance to pitting corrosion (particularly in 1.4404/1.4435)
• Manganese (Mn), silicon (Si) and carbon (C) in small proportions to control strength and weldability

Properties

The properties of the stainless steel must be retained after the colouring process or selectively enhanced through finishing.

Mechanical properties

Stainless steel is characterised by high tensile strength and ductility. Our PVD and nanoINOX® processes do not affect the mechanical properties of the base material. TiN (titanium nitride) coatings can even increase surface hardness, thereby improving wear resistance.

Physical Properties

The material has a density of approx. 7.9 to 8.0 kg/dm³. Thermal expansion and thermal conductivity must be taken into account when designing large-format, coloured façade elements to prevent stresses within the composite assembly.

Corrosion resistance

The natural corrosion resistance is based on the chromium oxide layer (passive layer). During colouring using the nanoINOX® process, this is supplemented by an additional sol-gel layer, which further increases chemical resistance and protects the steel from environmental influences.

Magnetism

The austenitic grades we primarily colour (e.g. 1.4301, 1.4404) are non-magnetic in the solution-annealed condition. Ferritic grades such as 1.4016, which we also finish, exhibit ferromagnetic properties.

Applications and Industries

Colored stainless steel from mirrorINOX is used in numerous sectors:

• Architecture & façade construction: Large-scale exterior cladding, roofing elements and solar shading systems in gold, bronze or black.
• Shopfitting & Interior Design: Display systems, counter cladding and wall panels, often combined with our VIBES or BEADS finishes.
• Yacht & Shipbuilding: Highly corrosion-resistant, colored components for exterior and interior applications (preferably grade 1.4404 or 1.4462 duplex).
• Elevator construction: Scratch-resistant, visually appealing cabin walls and control panels with anti-fingerprint properties.
• Product design: Enclosures for consumer electronics or premium household appliances.

Overview of international standard designations

The following equivalents apply to global sourcing and specification:

• 1.4301: AISI 304, SUS 304 (JP), X5CrNi18-10
• 1.4404: AISI 316L, SUS 316L (JP), X2CrNiMo17-12-2
• 1.4016: AISI 430, SUS 430 (JP), X6Cr17
• 1.4571: AISI 316Ti, X6CrNiMoTi17-12-2

Refining stainless steel – what mirrorINOX makes of it

At its Cleebronn site, mirrorINOX operates one of the world’s most advanced production facilities for stainless steel surface finishing. Since 2016, we have been producing reproducible finishes that meet the highest aesthetic standards in compliance with ISO 9001 certification.

We use two main processes for colouring stainless steel:

1. PVD/TiN coating: Using ARC evaporation under high vacuum, metals are vaporized and deposited onto the stainless steel surface as an extremely thin, hard layer. This produces shades such as champagne, gold, rose gold, bronze and anthracite. The process is environmentally friendly and completely free of toxic substances.
2. nanoINOX® coating: This process, based on sol-gel technology, applies layers with a thickness of 2 to 5 µm. Color pigments enable us to achieve an almost unlimited color palette, including Abyss Black (deep black) and custom colors. nanoINOX® offers functional benefits such as an anti-fingerprint effect (AFP) and easy-to-clean properties (ETC).

We finish grades ranging from 1.4016, 1.4301, 1.4401 and 1.4404 through to 1.4435, Duplex 1.4462 and 1.4571. Each sheet is inspected using spectrophotometric LAB colour measurement to guarantee a colour deviation of less than one point on the LAB scale. This ensures reproducibility, even for repeat orders. Our proprietary finishes such as Perfect Mirror No. 10® often form the basis for these high-end coatings.

• mirrorINOX Product Specifications PVD/TiN and nanoINOX®, 2024 edition.
• DIN EN 10088-2: Stainless steels – Technical delivery conditions.
• mirrorINOX quality management system in accordance with ISO 9001.
• Cleebronn site data, production since 2016.