Metal Marking Guide

How to laser engrave metal with a diode laser: spray marking technique

A 450 nm diode laser reflects off bare stainless steel — it cannot engrave it directly. The solution is to apply a thin coat of marking spray (moly lube, Cermark, or black tempera paint), let it dry, engrave at full power and slow speed, then wipe away the residue. For a 10W diode laser, a verified starting point is 70% power, 800 mm/min (13 mm/s), 1 pass, air assist OFF on stainless steel. The spray does the absorbing; the metal gets the permanent mark.

Why a diode laser can't engrave bare metal

The wavelength of a standard diode laser is around 450 nm (blue-violet light). Most metals — stainless steel, aluminium, copper, brass — are excellent mirrors at this wavelength. Stainless steel reflects around 55–65% of a 450 nm beam; polished aluminium reflects even more. The small fraction the metal does absorb is quickly carried away by the metal's thermal conductivity before it can create a visible mark.

The solution is a surface coating that's highly absorptive at 450 nm. When the laser hits the coating, the energy is absorbed locally, generating enough heat to chemically bond the coating compound to the metal surface. After engraving, you wipe away the unbonded coating — and only the laser-fused portion remains, permanently bonded to the metal.

Which metals work — and which don't need spray

Surface treatment options compared

Three products dominate hobbyist metal marking. They differ in cost, permanence, and cleanup method.

Step-by-step: the moly lube method

This is the most common approach for hobbyists. The material cost is low and the process is forgiving.

1. Degrease the metal surface. Wipe with isopropyl alcohol on a lint-free cloth. Fingerprints and oils prevent the coating from adhering evenly. Let it dry completely before spraying.
2. Mask the surrounding area (optional). Moly lube dries grey and can leave faint residue outside the engraving zone that's slightly harder to remove than Cermark. Masking tape around the work area saves cleanup time.
3. Apply first coat at about 25–30 cm distance. Move the can steadily across the surface — you want a thin, even grey film, not a pooled or wet-looking coat. Thin coats bond better; thick coats absorb too much laser energy and can prevent proper fusing.
4. Let dry 1–2 minutes. Moly lube dries quickly. The surface should look uniformly grey and matte. You can use a hair dryer to speed this to under 30 seconds.
5. Apply second coat perpendicular to the first. Two cross-coats give more uniform coverage than one. Let dry again.
6. Set your laser and engrave. Air assist OFF. See the settings table below. Run a 10 mm test square first at your intended settings before committing to the full design.
7. Remove residue. Dampen a cloth with IPA or acetone. Wipe the surface — the unbonded grey coating comes away easily. The laser-fused mark stays. Use nitrile gloves and ventilate when using acetone.

Step-by-step: the Cermark method

Cermark LMM-14 costs more but creates a ceramic-like bond that withstands dishwashers and heavier use. The application window is narrower — too thick or too thin both cause problems.

1. Degrease the surface with IPA. Same as moly lube — any oil or fingerprint causes the coating to pull away unevenly.
2. Mix paste with denatured alcohol (if using paste form). LMM-14 paste is mixed with denatured alcohol or distilled water — roughly 1 part paste to 2–3 parts liquid. Aim for a thin, paint-like consistency that sprays smoothly. Pre-mixed aerosol Cermark skips this step.
3. Spray from exactly 25 cm (10 in) distance. Start spraying before reaching the metal, move steadily, and stop spraying after passing it — constant velocity gives even coverage. One thin coat is enough. The correct coat thickness is 0.5–2 mils wet film — it should look uniformly grey, not wet or pooled.
4. Dry before engraving. Air-dry for several minutes naturally, or use a heat gun or hair dryer to bring it to dry in 10 seconds. The coating must be completely dry before the laser runs — wet coating doesn't bond properly.
5. Engrave at recommended settings. Same air assist OFF rule applies. Cermark settings are similar to moly lube (see table below) — start at the same power and speed, adjust slightly if marks look faint.
6. Rinse with water. The unbonded Cermark washes off with plain water and a cloth or soft brush. No solvents needed. The fused mark is dishwasher-safe at the rated temperature.

Laser settings for spray-marked metal

These are calibrated starting points — always test on a 10 mm square first. Air assist must be OFF; this applies to both moly lube and Cermark. See the full stainless steel settings leaf for a complete table by wattage.

If your mark rubs off with a fingernail after cleaning: increase power by 5–10% or slow speed by 20%. If your mark looks faint but doesn't rub off: the bond is likely good — adjust contrast in LightBurn by raising the DPI to 254 or the power slightly.

Cleaning up after engraving

The cleanup step is where most of the visual result happens — the mark looks muddled until the residue is removed.

• Moly lube residue: Wipe with a cloth dampened with IPA (isopropyl alcohol) or acetone. The grey coating lifts away cleanly. For complex contours or text, a cotton swab dipped in IPA reaches into fine detail. The fused mark stays put even with aggressive wiping.
• Cermark residue: Simply rinse under running water or wipe with a damp cloth. No solvents required — this is one of Cermark's practical advantages for production use.
• Tempera paint residue: Water and a cloth removes it. The engraved area may have a slightly lighter grey colour rather than a deep black — tempera creates a less permanent bond than chemical sprays.

Common mistakes and how to fix them

Frequently asked questions

Gear for metal marking

As an Amazon Associate I earn from qualifying purchases.