Plating and coating thickness in microns

At a glance

1 micrometre (µm) is a thousandth of a millimetre. We could not read the plating, anodising or powder-coat standards, so those figures are reported by secondary sources or missing. No life in years is given for any finish.

How thin is thin

A micrometre (micron, µm) is a thousandth of a millimetre, so 1 mm is 1,000 µm. A 1 mm brass strip therefore has 1,000 µm of metal to give. A 0.3 µm PVD film is about a three-thousandth of that, and a 25 to 38 µm lacquer film about a fortieth to a twenty-sixth.

The chart sets the figures we found on one scale. It is a log scale, so each gridline is ten times the last. The decorative finishes sit far to the left of the protective coatings. Solid green outlines are figures read in a maker's or trade-body document. Dashed grey outlines are reported by a secondary source and not confirmed. Dashed empty tracks mean no figure was sourced.

The PVD, colour-film and galvanising figures are the ones we trust most. PVD coatings explained gives the same PVD numbers with their sources; we have not changed them here. The lacquer figure belongs to one product, so treat it as an example of how a maker thinks about film thickness; see lacquered or unlacquered brass and copper.

What sits beneath matters as much as the film

A thin finish is only as good as what it sits on, and "brass finish" does not mean brass. One UK hinge maker's finish key lists polished and satin brass electroplate, lacquered, applied to stainless or mild steel. The coating house datasheet we read says brass, aluminium, zinc die-cast and ABS need nickel and chrome plating before PVD, so a brass-coloured PVD handle on a brass body carries plating under the PVD film, not one coating.

That is not a fault. It is a reason to ask. For any plated or coated metalwork, ask for the base metal, each layer and its thickness, the process, and the standard the thickness is measured to. Ask for them in writing, before the sample is approved.

Polish-through: what happens when the finish wears

Polish-through is the point where a thin layer has worn away and the layer beneath shows. On a handrail, push plate or handle it happens where hands land, first. What shows then is not the finish you specified. It is the next layer: nickel under chromium, or the base metal, or in the PVD-on-brass stack the nickel and chrome plating.

• Solid metal does not polish through. It can be re-polished, but the conservation guidance reminds us that polishing is abrasive, removes some surface metal and loses detail if repeated. Solid is not unlimited.
• PVD is hard, and its damage cannot be mended on site. Euro Inox says it is much more scratch resistant than electrochemical colouring, but that aggressive attack can damage the colour and that this damage is not repairable.
• No source we read gives a time to polish-through. It depends on the thickness, the hardness, what the metal touches and how often. Do not promise years. Ask the supplier for the certified minimum thickness and any wear test it has, and show the client a sample that has been deliberately worn.
• For rails, handles and thin inlays, a solid strip or part avoids the question. A plated strip is acceptable only where the client has been told that it will show its base in time. For brass inlay, see metal inlays.

What to put in a specification

• The base metal and its grade, and a statement if you do not want a zinc alloy or other cast base behind a plated finish.
• The process and each layer: for example nickel then chromium, or PVD over nickel and chrome.
• A certified minimum thickness for each layer, in micrometres, with the method used to measure it, where on the part it was measured and a certificate for each batch. We do not give a number to specify: take it from the current edition of the standard for the finish, or from the supplier's certificate.
• The standard and its class or service condition, with the edition (see the table below).
• The test and the acceptance criterion, including the duration of any salt-spray test, written in because the test standard does not set one.
• A worn sample for any finish that will be handled, so the client sees what polish-through looks like before approving.
• No life in years unless the supplier states one in writing.

Which standard to name for each finish:

All standards above are named, not quoted. Confirm each against the current edition before use.

[Element]: base metal [solid brass CW508L / stainless steel grade / steel], not [zinc alloy]. Finish: electroplated [nickel and chromium] to [BS EN ISO 1456, edition to be confirmed], service condition [__], minimum thickness [__] micrometres nickel and [__] micrometres chromium, certified by the plater with the measurement method and a certificate for each batch. Corrosion test [ISO 9227, __ hours, edition to be confirmed] on a production-representative sample. Colour approved on sample [ref. __].

PVD [colour, ref. __] on [stainless steel grade / brass with nickel and chrome underlayer]. Minimum thickness [__] micrometres, certified with the measurement method and a certificate for each batch. Underlayer thickness [__] micrometres certified. Base finish [code] approved before coating. See TL-MET-04 for the full wording.

[Element]: solid [brass CW508L], [__] mm thick, unplated and uncoated, finished [satin / polished] to approved sample [ref. __]. Not plated base metal. Allow for re-polishing [__] times without exposing a different material.

For each plated or coated finish: base metal and grade; each layer and process; minimum thickness per layer with the measurement method and the locations measured; the standard and class; test reports [__]; a worn or abraded sample [ref. __] where the finish will be handled. No service life is implied unless stated by the supplier in writing.

Standards and sources

• A coating manufacturer's decorative PVD datasheet: 0.2 to 2.0 micrometres, 1,500 to 2,800 HV; brass, aluminium, zinc die-cast and ABS need nickel and chrome plating first; read 5 November 2026.
• Euro Inox, Colouring Stainless Steel (Materials and Applications Series, Vol. 16, 2011): electrochemical film 0.02 to 0.36 micrometres; PVD typically about 0.3 micrometres; not repairable; BSSA-hosted.
• Galvanizers Association: EN ISO 1461 coating thicknesses (2022 edition): local and mean minimum thickness by steel thickness.
• Canadian Conservation Institute, CCI Notes 9/3 (2007): polishing is abrasive and removes some surface metal.
• A lacquer maker's data sheet; a hinge maker's finish key; a UK supplier's anodising article: lacquer film thickness; brass-electroplate finish codes; anodising classes (secondary).
• BS EN ISO 1456, BS EN ISO 7599:2018, BS EN 1670, ISO 9227, EN 1811: named, not read: confirm the current editions.

Questions we are asked

How thick is PVD compared with plating?

PVD is 0.2 to 2.0 micrometres on one coating house's datasheet, with about 0.3 micrometres typical per Euro Inox. A decorative chromium layer is reported at a fraction of a micrometre too, over a nickel layer whose minimum the standard sets by service condition. Ask for each layer.

Is a "brass finish" handle solid brass?

Not necessarily. Finish keys include polished and satin brass electroplate, lacquered, applied to steel or stainless. Ask for the base metal, and write "solid brass" into the specification if that is what you need.

How long before a plated finish wears through?

No source we read gives a time. It depends on the layer thickness, the hardness, the base and how often the part is touched. Ask the plater for the certified minimum thickness and any wear test, and never write a life in years.

What minimum thickness should I write?

The certified minimum from the standard for the finish and the supplier's process, for each layer. We do not give a number here, because the standards for plating, anodising and powder coat were not read. For PVD, see our PVD sheet.

What will show when the finish wears away?

The layer beneath: for plated work usually nickel, or the base metal; for PVD on brass the nickel and chrome plating. Ask what colour that is and show the client a deliberately worn sample.

Should inlay strips and rails be solid or plated?

Solid, wherever they will be handled or may need re-polishing. A plated strip is acceptable only where the client accepts that its base will show in time.