- Laser engraving removes material.The beam vaporises the surface and leaves a groove you can feel, typically up to about 0.5 mm deep.
- Laser etching melts the surface.The molten metal swells into a shallow, slightly raised mark, about 0.025 mm high.
- Laser bonding fuses a mark onto the surface.A marking coating is fused to the steel where the beam hits. The mark is deep black and holds up to UV, salt spray and chemicals outdoors.
"Laser marking" is the umbrella term for all of them, which is where most of the confusion starts. For tags that are read outdoors for years, bonding is usually the one to specify, so it gets the most space below.
Laser engraving
The beam heats the surface past its boiling point, so the material vaporises and leaves a cavity. Several passes cut deeper. Engraving gives the most permanent result. A groove stays readable after the surface is scratched, worn or painted over.
- Vaporise. The beam heats the steel past boiling point.
- Remove. The material leaves as vapour and fine debris.
- Repeat. Each pass cuts deeper.
On stainless steel the groove is the same colour as the metal around it, so an engraved tag can be hard to read from a distance. The usual fix is infill: the groove is filled with paint or enamel in a contrasting colour. Outdoors, that infill is the part that weathers. The groove lasts, but the paint in it can fade or chip.
- Depth: typically up to about 0.5 mm, deeper with more passes.
- Use it for: tags that face abrasion, grit-blasting, heavy handling or overpainting.
Laser etching
Etching is a lighter form of engraving. The beam melts the surface instead of vaporising it. The melted metal expands and sets as a slightly raised, roughened mark. Depending on the surface finish and laser settings, it reads as black, white or grey.
- Melt. The beam melts a thin skin of the surface.
- Swell. The molten metal expands upward.
- Set. It cools into a rough, raised mark.
Etching is popular for part serials and barcodes on production lines. Because the mark is so shallow, it wears off sooner under abrasion and weather.
- Depth: about 0.025 mm (0.001 in).
- Use it for: serial numbers, codes and barcodes on parts kept indoors or handled lightly.
"Etched" doesn't always mean laser. When a supplier quotes an etched stainless steel nameplate, they may mean chemical etching. Acid eats into the steel through a stencil, and the recesses are then paint-filled. It gives a deep, durable mark but isn't a laser process at all. Ask which one you're getting.
Laser bonding
Bonding adds a mark instead of cutting or melting one. It starts with a marking coating on the tag. The laser fuses the coating to the steel wherever it hits, and the rest is wiped away. What's left is a deep black, high-contrast mark that is part of the surface, not ink on top of it.
- Coat. A marking coating covers the tag.
- Fuse. The beam bonds the coating to the steel where it hits.
- Wipe. The unfused coating wipes off.
Why it holds up outdoors
An outdoor tag has to stay readable through sun, rain, salt and the occasional splash of fuel or cleaner. Bonded marks are tested for exactly that:
- UV: no fading or discolouration in outdoor exposure, and it holds up to weathering in QUV testing.
- Chemicals: no effect after a week in organic solvents, or in acids and bases except 35% hydrochloric acid.
- Environment: resists salt spray, heat, cold and scratching.
Because the mark is black on bright steel, it reads from further away than an unfilled groove, and there's no paint infill to fade.
- Depth: a thin layer on top of the steel. You can barely feel it.
- Use it for: outdoor tags, offshore and marine equipment, and anything exposed to salt spray or chemicals that must be read from a distance.
The extra step with bonding is the coating, and coating each tag yourself before marking is extra work. Our coated SS316 tags come with the coating already applied, ready for the laser.
Laser annealing
Annealing is the other way to mark stainless steel black. Nothing is added: the beam heats the steel below its melting point, and a dark oxide layer grows in the surface.
- Heat. The beam warms the steel, below melting point.
- Oxidise. An oxide layer grows in the surface. It runs straw, brown, purple and blue as it thickens.
- Stop at black. The settings hold it at a dark, even colour.
Annealing needs no coating, but it has a catch on stainless. The heat that makes the mark can weaken the steel's protective oxide film at that spot, and passivating the part afterwards can lighten the mark. Bonding doesn't rely on growing an oxide layer, and it gives a deeper black.
Side by side
| Engraving | Etching | Bonding | |
|---|---|---|---|
| What happens | Material vaporised | Surface melted | Coating fused on |
| Depth | Up to ~0.5 mm | ~0.025 mm, raised | Thin layer on top |
| Can you feel it? | Yes, a groove | Slightly | Barely |
| Contrast | Low unless infilled | Medium | High (black) |
| Survives abrasion | Best | Poor | Good |
| Outdoor weathering and UV | Groove lasts; infill paint can fade | Shallow mark weathers sooner | No fading in UV; tested in QUV weathering |
Which one to specify
Start from what the tag has to survive, not from what the laser can do.
Whichever you choose, write the method on the specification. "Laser marked" alone could mean any of them.
Definitions
- Laser engraving
- Removes material to cut a groove, typically up to about 0.5 mm deep. Very wear-resistant, but low contrast unless the groove is infilled with paint.
- Laser etching
- Melts a thin layer of the surface into a slightly raised mark, about 0.025 mm high. Shallow, so it wears and weathers sooner.
- Laser bonding
- Fuses a marking coating onto the metal to form a permanent black mark. High contrast, no fading in UV, resists salt spray and chemicals; the better choice for outdoor tags.
- Laser annealing
- Heats stainless steel below its melting point so an oxide layer darkens the surface. No coating and no depth; can weaken the steel's corrosion resistance at the mark.
Questions
Which laser mark lasts longest on an outdoor tag?
Against abrasion, engraving, because the groove stays readable after the surface wears. Against chemicals and salt spray, with a high-contrast mark, laser bonding.
How do you laser mark stainless steel black?
Either by annealing, which grows a dark oxide layer in the surface, or by bonding, which fuses a coating onto it. Annealing needs no consumables. Bonding gives a deeper black and better chemical resistance.
Is laser etching the same as laser engraving?
No. Engraving vaporises material and leaves a groove, typically up to about 0.5 mm deep. Etching only melts the surface into a shallow raised mark about 0.025 mm high. Etching is faster; engraving survives far more wear.
Does laser marking affect stainless steel's corrosion resistance?
Annealing can. The heat can weaken the protective oxide film at the mark, and passivating afterwards can lighten the mark. Engraving and bonding don't rely on growing an oxide layer.
Is laser bonding the same as laser annealing?
No. Both give a black mark on stainless steel, but they are different processes. Annealing heats the steel so its surface oxidises dark, with no coating. Bonding fuses a marking coating onto the steel. Annealing can weaken the steel's corrosion resistance at the mark; bonding doesn't rely on growing an oxide layer.