Quick Answer: A standard diode or CO2 laser can’t mark bare metal directly because the beam mostly reflects off the surface — only a 1,064nm fiber laser does that. Diode and CO2 owners work around it with a marking spray like Cermark or dry-moly lube, which bonds a permanent dark mark under laser heat, but the single most common reason those marks fail is running air assist on, which blows away the exact heat the coating needs to fuse (per LaserTinkerer’s diode-metal testing). Dry moly lube costs about $10-13 a can and holds up nearly as well as $60+ Cermark for most craft work — Cermark only earns its price on items that need to survive a dishwasher.
Metal is the one material where “just turn up the power” doesn’t work, because the problem isn’t strength, it’s physics — most laser wavelengths simply bounce off bare metal instead of marking it. This guide covers why that happens, real settings by laser type, the marking-spray workaround for diode and CO2 owners, and the one setup mistake (air assist) that silently ruins more metal-marking jobs than a wrong power setting ever does.
Why metal reflects instead of marking
A laser marks a material by having its energy absorbed as heat; metal’s problem is that most common laser wavelengths don’t get absorbed, they bounce off. A 450nm blue diode beam reflects off most polished and raw metal, and a CO2 laser’s 10,600nm beam is reflected by polished metal almost entirely. Stainless steel alone reflects an estimated 55-65% of blue diode light, per LaserTinkerer’s diode-metal testing — which is why a diode or CO2 laser aimed at bare steel with no prep leaves nothing behind at all, no matter how high you push the power.
A 1,064nm fiber laser is the exception: bare metal absorbs that wavelength efficiently enough to mark directly, no coating needed (see our best fiber laser engraver roundup for picks). Anodized or powder-coated metal is a separate case — the coating itself engraves like a painted surface on any diode or CO2 laser, since the beam is marking the coating, not the bare metal underneath. Bare, uncoated metal is the real gap, and it’s what the rest of this guide covers.
Settings by laser type
| Laser | Power | Speed | Notes |
|---|---|---|---|
| 10W diode + spray | 70-80% | 800-1,000mm/min | 1 pass, air assist OFF |
| 20W diode + spray | 80-90% | 800-1,500mm/min | 1 pass, air assist OFF |
| 35W CO2 + spray | 100% | Speed 30 | Per-machine speed scale, not mm/s |
| 50W CO2 + spray | 100% | Speed 40 | Per-machine speed scale, not mm/s |
| Fiber, bare stainless | 40-60% | 200-500mm/s | 20-50kHz, 1-3 passes, no spray needed |
These are starting points from LaserTinkerer’s diode testing and StyleCNC’s CO2 settings guide, not fixed numbers — spray brand, tube or diode condition, and the specific metal all shift the right settings. Burn a test grid on scrap metal from the same batch before committing to a finished piece; see our laser engraver settings guide for how to structure that test across a power/speed range.
Need marking spray or scrap metal on hand before a batch job? check current price on Amazon →. Running an engraving business? A free Amazon Business account unlocks quantity discounts and tax-exempt purchasing on the spray cans, blanks, and metal stock you’ll be reordering constantly.
The air-assist mistake
This is the single most common reason a metal-marking job fails, and it has nothing to do with power or speed. Marking sprays like Cermark and dry-moly lube work by bonding to the metal under laser-generated heat — the beam heats the coating, and that heat fuses it permanently to the surface. Air assist’s entire job on a normal cutting or engraving pass is the opposite: it blows a jet of air across the work area to clear smoke, debris, and heat buildup.
Run air assist during a spray-marking job and you’re blowing away the exact heat the coating needs to bond, per LaserTinkerer’s testing — the mark can look fine right off the machine and then wipe or flake off under light handling, because it was never fully fused to the metal. Turn air assist off for any spray-marking job, even if it’s your default setting for everything else you run. It’s an easy setting to forget precisely because most machines default to air assist on, and metal is the one material where that default actively works against you.
Cermark vs. dry-moly lube: which spray to buy
| Spray | Cost | Bond | Best for |
|---|---|---|---|
| Dry moly lube (CRC 3084) | $10-13/can | High, resists acetone | Gifts, craft work, stainless steel |
| Cermark LMM-14 | $60+ | Ceramic bond, very high | Commercial items, dishwasher-safe pieces |
| Black tempera paint | $2-5 | Medium, less durable | Testing and prototyping only |
Dry moly lube — sold as an automotive anti-seize/lubricant spray rather than a laser product, CRC 3084 is the commonly cited brand — costs a fraction of Cermark and, per LaserTinkerer’s side-by-side testing, bonds a mark to stainless steel that’s nearly as durable and resists acetone well. For most gift and craft orders, that’s the better value. Cermark LMM-14 earns its higher price with a true ceramic bond, which is what matters for anything that goes through repeated dishwasher cycles or heavy commercial handling — a mark on a stainless tumbler someone hand-washes has different requirements than a nameplate that gets scrubbed daily. Black tempera paint is cheap enough for a quick settings test on scrap but isn’t durable enough for a finished piece.
One more caveat worth knowing before you commit to a coating-and-spray workflow: copper and brass conduct heat away from the mark site much faster than steel does, which can dissipate the heat a spray needs to bond before it fuses — both metals are flagged as genuinely difficult in LaserTinkerer’s testing, even with the same spray and settings that work cleanly on stainless. If brass or copper marking is more than occasional work, see our best laser engraver for brass guide, where a fiber laser’s direct bare-metal mark sidesteps the whole spray-and-heat-dissipation problem.
The bottom line
Bare metal reflects most laser wavelengths instead of absorbing them, which is why a diode or CO2 laser needs a marking spray — Cermark, dry-moly lube, or similar — to leave a permanent mark, while only a fiber laser marks bare steel, brass, or aluminum directly. Whichever spray you use, turn air assist off; it’s the single most common reason a spray mark fails to bond, and it’s easy to forget precisely because most machines default to it being on. Dry moly lube at $10-13 a can covers most craft and gift work; save Cermark’s $60+ ceramic bond for pieces that need to survive a dishwasher. And if brass or copper marking becomes a regular part of your catalog rather than an occasional job, a dedicated fiber laser sidesteps the coating step entirely — see our best laser engraver for metal and best laser engraver for stainless steel roundups for picks, or our laser engraving materials guide for how metal compares to wood, acrylic, and the other materials a laser handles.