At a glance

RouteHow the colour is madeWear and repairWelding and forming after
Interference (electrochemical) colourA hot acid bath thickens the steel's own clear oxide film to 0.02 to 0.36 µm, then it is hardened. Light interference gives bronze, gold, red, purple, blue, green on austenitic steel (ferritic: dark grey only). Colour shifts with the viewing angle.No fade in sunlight. Abrasion removes it: not for high-traffic areas. No repair on site: replace the panel.Bends (the film thins at the bend). Welding destroys the colour. Screws, rivets, clamps, adhesive are fine.
Black oxide (blackening)A molten sodium dichromate salt bath at about 400 °C leaves a thin, smooth, dull black oxide film. Any stainless type. Black only.Does not age; good abrasion resistance; removed by corrosion or heavy abrasion. For small parts and handles needing a tougher black.Ductile: moderate forming does no harm.
PVDA ceramic layer, typically 0.3 µm, vaporised on to the finished surface in a vacuum chamber. Gold, rose gold, bronze, blue, black, wine red. Colour does not change with the angle.Much more scratch resistant than interference colour, not scratch proof. Aggressive damage is not repairable.Weld before coating. If formed after coating, make acceptance subject to a bend test.
Coil coatedPrimer and a clear or opaque top coat rolled on to the coil in the factory. Wide colour range, close matching, anti-fingerprint varnish possible. Minimum order quantities.Adds no corrosion resistance; the steel still protects scratches and cut edges. Repair not covered by the source.Bendable. Treated as non-weldable (follow the supplier's rules if unavoidable). Adhesive bonding works well.
Painted after fabricationAny colour, for looks not protection. Remove the passive film shortly before painting; use an etchant primer.The usual failure is lost adhesion. A scratch is not enlarged by corrosion. Repainting depends on matching the colour.Paint after welding and forming.
Etched, with colourA printed or silk-screened mask, then acid etching removes a little metal: dull, slightly coarse against polished. Interference colour before or after etching, or paint in the recess.Etching, pickling and electropolishing remove interference colour, so order matters. Colour left in the recess is less exposed.Depends on the colour route chosen: ask the finisher.

As stated by Euro Inox (2011 and 2005 guides). No prices: ask the partner to price each route.

Six routes, and the one split that matters

Euro Inox, the European stainless steel development association, sets out the ways of colouring stainless steel in its guide Colouring Stainless Steel (Volume 16, 2011). “Electrochemical” and “interference” colouring are two names for one route: the colour comes from light interfering inside a thin, transparent film, in the same way as oil on water. This sheet puts that route beside the others, and adds etched patterns from Euro Inox's finishes guide.

The split that matters is between a film grown from the steel and a layer added to it. Interference colour and black oxide thicken or convert the steel's own oxide surface. PVD, coil coating and paint put something new on top. The two thinnest routes are similar in size, since interference films are 0.02 to 0.36 µm and PVD is typically 0.3 µm (both Euro Inox), but they do not behave alike. Euro Inox says PVD is much more scratch resistant than electrochemical colouring and that its colour does not change with the viewing angle. Interference colour does change: the angle of the light, and the curving of a panel, change the apparent colour, so Euro Inox suggests splitting a large curved surface into small flat panels if a very even colour is wanted.

Interference colour is also the one route where corrosion costs you the colour. Even light corrosion of a coloured surface can leave a permanent colour change, and removing the corrosion removes the colour. Euro Inox's advice is to choose a stainless chemistry that will not corrode in its setting: see 304 or 316 stainless steel. It also reproduces a 1992 test on coloured 304 (its Table 1) in which the colour did not change in 5 per cent neutral detergent, 5 per cent sodium carbonate, 5 per cent caustic soda, acetone, lacquer thinner, trichloroethylene or soy sauce, for the times and temperatures given, and changed slightly in cement water at 100 °C after 10 hours.

Sample board of six ways to colour stainless steelSix sample tiles side by side, each with a colour swatch above and a section through the layers below. 1: interference colour, a transparent oxide film grown from the steel's own surface, 0.02 to 0.36 micrometres, colour shifts with viewing angle. 2: blackening, a thin dull black oxide film from a hot salt bath. 3: PVD, a separate ceramic layer added on top, typically 0.3 micrometres. 4: coil coating, primer and top coat applied to the coil in the factory. 5: paint applied to the fabricated piece over an etchant primer. 6: etched pattern, with colour or paint left in the recesses and the high points polished. Swatch colours are illustrative and layers are not to scale.InterferencecolourFilm 0.02 to 0.36 µmShifts with the angleBlack oxide(blackening)Dull black filmBlack onlyPVDAbout 0.3 µm, ceramicAdded on topCoil coatedApplied on the coilColour matches wellPaintedApplied after makingAdhesion is the riskEtched(with colour)Matt against polishColour in the recess
Six colour routes as a sample board, with a section through the layers of each. Swatch colours are illustrative, not matches; layers are not to scale. Original drawing by Make Bespoke Studio, from Euro Inox, Colouring Stainless Steel (2011).

Choosing by use: lifts, doors, bar fronts and wall panels

Start from how the surface will be treated, then how it is made. The chart takes the questions in order and the first “yes” gives the answer. It is our reading of the Euro Inox statements below, not a rule in any standard.

  • Lift cars and column covers. Euro Inox says decorative sheets with a PVD layer are often used for elevators and column covers where pedestrian traffic can be expected. It says interference colour should not be used where accidental or deliberate damage can occur, such as in a high-traffic area.
  • Doors and handles. PVD has been used on door hardware, but Euro Inox warns that the colour can be damaged if it is attacked aggressively, and that this damage is not repairable.
  • Bar fronts and counters. No source we read rates any route for a bar front, which is knocked, wiped and sanitised every day. Treat it as the hardest case, ask the partner workshop for its finisher's evidence, and decide in advance how a damaged panel will be replaced. See also high-touch hospitality metal finishes.
  • Wall panels. Euro Inox lists interference-coloured sheet for internal cladding in low-traffic areas, signs and shop display panels. Coil-coated sheet is listed for architectural and decorative panels, furniture and doors, and gives the closest colour match across a large area.
  • Small black parts. Black oxide is a more scratch-resistant black than interference colour, and has been used for small architectural components and flatware handles.
  • Any colour or pattern a film does not give. Paint, or an etched pattern with colour left in the recess.
A first filter for choosing a colour route for stainless steelFour questions in order. 1: will welding be done on the piece? Then weld first and colour afterwards with PVD or paint, because interference colour does not survive welding and coil-coated sheet is not weldable. 2: will it be touched, rubbed or knocked often, as in a lift, a door or a handle? Then PVD, or black oxide for small black parts; interference colour is for low-traffic places. 3: is it a large matched area or does it need an anti-fingerprint surface? Then coil-coated sheet. 4: is it a low-traffic wall or soffit where the colour should shift with the light? Then interference colour, with large samples in the project light. A bottom band says that no route can be repaired on site, so plan for panel replacement.1 Will welding bedone on the piece?YesWeld first, thenPVD or paint.Interference colourdoes not survivewelding.No2 Will it be touched,rubbed or knocked often?(lift, door, handle)YesPVD for hard wear.Black oxide for smallblack parts.Not interferencecolour.No3 A large matchedarea, or an anti-fingerprint surface?YesCoil-coated sheet:close colour match,clear varnishoption. Minimumorder sizes apply.No4 A low-traffic wall,where the colour shouldshift with the light?ThenInterference colour.Approve large samplesin the project light.Split curved facesinto flat panels.Any colour or pattern a film does not give: paint, or etch and leave colour in the recess.Every route: colour cannot be repaired on site, so plan for panel replacement.
A first filter for choosing a colour route. Drawn from Euro Inox, Colouring Stainless Steel (2011); the order of the questions is ours. Original drawing by Make Bespoke Studio.

What every route shares

  • The base finish shows. Interference films and PVD are so thin that the finish beneath decides the look: Euro Inox says a dull finish gives a subdued, matt colour and a mirror polish a brightly coloured one. Fix the finish first, by its EN 10088-2 code and a measured roughness, as set out in stainless finish codes.
  • Nothing is repaired on site. For interference colour and PVD Euro Inox says repair can only be achieved by replacing the panel. Order spare panels with the run, because colour can vary from batch to batch (Euro Inox, finishes guide), and see spares and attic stock.
  • Approve large samples in the real light. Euro Inox advises viewing samples under the actual lighting at the building, and keeping a larger sample as the visual standard for the project once specifier and supplier agree. For the sample steps see metal finish sample approval and batch variation.
  • Make before you colour. Welding is done before PVD, and interference colour does not survive it. Bending after colouring is possible for interference colour and needs a bend test for PVD.
  • Clean gently. Mild detergent and water, a soft cloth or a soft-bristle plastic brush, no metallic brushes or abrasive compounds, and low-pressure hosing in place of high-pressure jets, which may damage the colour. Wash cement or mortar splashes off at once, because alkali can discolour coloured finishes. Leave graffiti to a specialist cleaner. The routine is in cleaning and maintaining metal finishes.
  • Strippable film has a life. Euro Inox says not to exceed the film's recommended maximum life before stripping it, or adhesive can be left on the surface.

How to specify and approve it

EN 10088-2 does name a finish for colour. Euro Inox says Table 6 of EN 10088-2:2005 uses the designation 2L (special finish) for coloured flat products. That restricts the starting material to cold rolled, requires only one side to meet the agreed colour tone and surface quality, and leaves the colour itself to be agreed between specifier and supplier. The 2005 edition was withdrawn in October 2014 and BS EN 10088-2:2024 is now current (BSI), so confirm that 2L is unchanged in the current text before you quote it.

  • Name the route, the grade and the base finish, not just the colour.
  • Fix the colour by an approved physical sample. For painted and coil-coated work a paint reference can be added: see RAL, BS 4800 and NCS colour references. For PVD, thickness and test wording are on the PVD coatings sheet.
  • Say what happens after colouring: no welding for interference colour, welding before coating for PVD, a bend test on receipt if PVD is formed.
  • Ask which routes the partner workshop's finishers actually supply, and what size a single piece can be. This sheet gives no panel-size limits, because none were published for the processes it describes.

Specification wording

Paste into your schedule or specification and replace anything in [square brackets] with your own figures. Wording is a starting point: your specification governs.

Interference-coloured stainless panel
Stainless steel sheet, grade [1.4301 (304); 1.4401 (316) where chlorides reach the surface], [1.2] mm, cold rolled, colour finish designation [2L] to EN 10088-2 (edition [to be confirmed]), on a base finish of [2J brushed / 2P mirror] approved before colouring. Colour by electrochemical (interference) colouring, [colour name], matched to approved large sample [ref. __] viewed under [project lighting] within [tolerance agreed with the finisher]. All panels in one visible run from the same batch, grain [vertical]. No welding, brazing or abrasion after colouring. Fixed by [screws, rivets, clamps or adhesive]. Strippable film removed within its recommended life. Spares: [__] from the same batch.
PVD, coil-coated or painted stainless
Colour by [PVD (wording as the PVD coatings sheet) / coil-coated sheet / paint], [colour name or reference] matched to approved sample [ref. __]. Coil-coated: [supplier's system ref. __], one coil batch per visible run, no welding in coated areas. Painted: welding and forming complete first; passive film removed and etchant primer applied [as the paint supplier directs]; paint system [by the paint supplier].
Approval, damage and care
Full-size samples [300 x 300 mm] of each colour on each base finish approved under [project lighting] and kept as the visual standard. Colour cannot be repaired on site: damaged panels replaced by [__]. Clean with warm water and mild detergent, soft cloth or soft plastic brush. No metallic brushes, abrasives, chloride-containing cleaners or high-pressure jets. Wash cement and mortar splashes off at once.

Terms used on this page

Interference colour (electrochemical colouring)
Colour made when light reflects inside a thin transparent oxide film on stainless steel, as with oil on water. The film is thickened in an acid bath and then hardened. The apparent colour changes with the angle of view.
Passive film
The thin, invisible chromium oxide layer that gives stainless steel its corrosion resistance and repairs itself in air. Interference colour thickens it; paint needs it removed first.

All metalwork terms

Standards and sources

Questions we are asked

What is the difference between PVD and electrochemical coloured stainless steel?

Electrochemical (interference) colour thickens the steel's own clear oxide film so that light interference shows a colour, and the colour shifts with the viewing angle. PVD adds a separate ceramic layer, typically 0.3 micrometres, whose colour does not change with the angle. Euro Inox says PVD is much more scratch resistant. Neither can be repaired on site.

Is coloured stainless steel hard wearing enough for a lift or a door?

PVD is the one Euro Inox links to elevators, column covers and door hardware, with the warning that aggressive attack can damage the colour and that this cannot be repaired. Interference colour is not for high-traffic areas, because abrasion removes it. Ask the partner workshop for its finisher's wear evidence before you commit.

Can coloured stainless steel be welded or bent?

Interference colour cannot be welded without destroying the colour, though it can be bent, and the film thins slightly at the bend. For PVD, weld first and coat afterwards, and make acceptance subject to a bend test if it is formed after coating. Coil-coated sheet is treated as non-weldable, but adhesive bonding works well.

Does coloured stainless steel fade in sunlight?

Not through the film routes Euro Inox describes. With no pigment to bleach, interference colour does not fade, and Euro Inox reports no colour change in electrochemically coloured roof panels after 30 years. Paint is different: the steel under it is far more durable than the paint, which will eventually need renewing.

Can a scratch in coloured stainless steel be repaired?

Not on site for interference colour or PVD: Euro Inox gives panel replacement as the repair. A scratch in paint can be repainted if the colour can be matched. Plan spare panels from the same batch.

Is there a standard for the colour?

Euro Inox says EN 10088-2 (2005 edition) uses the finish designation 2L for coloured flat products but does not set colours: the colour is agreed between specifier and supplier. Fix it by an approved sample viewed under the project lighting.

Can any stainless steel be coloured by interference?

Euro Inox says austenitic grades are particularly suited and that ferritic grades can only be coloured dark grey by this process.

Download the factsheet

A two-page A4 PDF with the six routes compared, the sample board and first-filter chart, and specification wording to keep with your project file.

Factsheet TL-MET-34 v1.0 (PDF)