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Marking bare metal with a diode laser
A 450 nm diode will not put a permanent mark on bare stainless or aluminium by itself. With a marking spray it will - the spray does the absorbing and fuses a ceramic layer to the surface. Here is what that involves, what it costs, and where the method runs out.
Why bare metal defeats a diode
Two things work against you. Polished metal reflects a large share of 450 nm light rather than absorbing it, and what does get absorbed is spread across a spot that is not tight enough to reach the power density needed to melt or oxidise steel. The beam heats the surface a little and the metal, being an excellent conductor, carries that heat away almost as fast as you deposit it.
A fiber laser sidesteps both problems. At 1064 nm metals absorb far more readily, and a galvo head focuses to a much smaller spot, so peak power density is orders of magnitude higher. That is why fiber is the metal tool and diode is not.
There is one important exception. Anodised aluminium is not bare metal - it carries a dyed oxide layer, and a diode ablates that dye cleanly to expose the pale aluminium underneath. No spray needed. If your job is anodised, you already have what you need; see our anodised aluminium settings.
What marking spray actually does
Commercial marking compounds - CerMark and LaserBond are the names you will see, along with several own-brand equivalents - are suspensions of metal oxides in a carrier. You coat the part, let it dry, and fire the laser at it. The laser supplies enough heat to fuse the compound into the surface, forming a hard, dark, permanently bonded layer. You then wash the unfused excess away.
The crucial point: the mark is not engraved. Nothing is removed. You have bonded a thin ceramic coating in the shape of your artwork. That has consequences for durability, and it means a fingernail test tells you nothing useful - a good bond will pass that and still wear at the edges over years of handling.
The DIY alternatives, honestly
Dry molybdenum disulfide lubricant spray is the widely-repeated cheap substitute, and it does produce marks. Expect it to be less consistent and less durable than a purpose-made compound - the particle size and binder are not designed for this. It is a reasonable way to find out whether the method suits your work before buying a bottle of the real thing, not a production answer.
Treat any recipe involving household paints or powders with suspicion. Heating unknown coatings produces unknown fumes, and some of them are genuinely nasty.
Which metals respond
| Metal | With marking spray | Notes |
|---|---|---|
| Stainless steel | Very good | The best case. High contrast, sharp edges. |
| Mild / carbon steel | Good | Clean and de-grease thoroughly first. |
| Titanium | Good | Marks well; a fiber does it better and in colour. |
| Bare aluminium | Fair | Conducts heat away fast; slow down, expect softer edges. |
| Brass / copper | Poor | Very reflective, very conductive. Frustrating. |
| Anodised aluminium | No spray needed | Diode ablates the dye directly. |
Method and settings
- Degrease properly. Isopropyl alcohol, then do not touch the face with your fingers. Skin oil is the single most common cause of patchy marks.
- Coat thinly and evenly. Thin matters more than opaque. A thick coat insulates the surface from the heat it needs and gives a grey, weak mark.
- Let it dry completely. Firing at a damp coat pops and spatters.
- Focus carefully. Metal marking is far less forgiving of focus error than wood; run a ramp test if you are not certain.
- Wash and inspect. Unfused compound rinses off with water and a soft brush.
Starting points for a 10-20 W diode on coated stainless. These are a place to begin a test grid, not settings to trust:
| Parameter | Starting value |
|---|---|
| Speed | 200-600 mm/min |
| Power | 90-100% |
| Line interval | 0.05-0.08 mm |
| Passes | 1-3 |
Slow and dense is the shape of it. If the mark comes out grey rather than black, the usual causes are a coat that is too thick, focus that is off, or speed that is too high - in that order of likelihood.
Durability, and the honest limits
A well-fused mark on stainless survives handling, dishwashers and outdoor exposure. A poorly-fused one lifts at the edges within months. The difference is almost entirely coat thickness and focus, which is why the test grid matters more here than on wood.
Where the method runs out is throughput. Every part needs degreasing, coating, drying, marking and washing. That is five handling steps per piece, and the consumable is not cheap. For a handful of parts that is fine. For a few hundred it is miserable, and the maths starts to favour a machine that marks bare metal directly.
Our fiber marking calculator works out the per-part cost of doing it on a fiber, and the ROI calculator tells you how many parts it takes for that machine to pay for itself. Run your real volume through both before buying more spray.
FAQ
Can a diode laser engrave stainless steel?
Not bare. A 450 nm diode is largely reflected by polished metal and cannot reach the power density needed to mark it. With a marking spray such as CerMark or LaserBond it produces a permanent bonded mark on stainless, which is the standard workaround.
What is laser marking spray and how does it work?
It is a suspension of metal oxides that you coat onto the part and dry. The laser fuses the compound into the surface, leaving a hard dark layer bonded to the metal. Nothing is engraved or removed - the mark is an added ceramic coating in the shape of your artwork.
Does molybdenum disulfide spray work instead of CerMark?
It does produce marks and is a cheap way to test whether the method suits your work. Expect less consistency and less durability than a purpose-made compound, because the particle size and binder are not designed for the job. It is not a production answer.
Do I need marking spray for anodised aluminium?
No. Anodised aluminium carries a dyed oxide layer, and a diode ablates that dye directly to expose the pale metal underneath. It is one of the few metal-looking jobs a diode does well with no coating at all.