Short answer: A fiber laser black-marks stainless steel by heating the surface just enough to grow a dark oxide layer under it (annealing), so the part stays smooth and no metal is removed. Brass turns dark when the laser changes its surface at high power with a very tight line spacing. Our Edge 50W preset for black on stainless runs at 30% power, 102 mm/s (4 in/s), 60 kHz with a 0.025 mm line interval on the 220mm lens. Because a black mark has essentially no depth, it is a cosmetic or ID mark, not a substitute for the .003" deep engraving ATF requires for serial numbers and other required markings.

What "black marking" actually is

Most firearm laser work removes material: you vaporize coating or metal to cut a mark you can feel. Black marking is different. On stainless steel, the laser heats a thin zone below the surface. That heat drives oxidation, and the oxide layer reflects light differently, so you see a dark gray to jet black mark. This process is usually called annealing marking.

The appeal for a gun shop is obvious: the mark is smooth to the touch, high contrast, and does not create a groove that can collect oil, carbon, or cleaning residue. It looks finished and clean on polished or bead-blasted stainless, which is why customers like it for logos, slide art, and personalization.

The color comes from heat, not from depth. Lower speed and tighter line spacing put more heat into each spot. Too little heat and the mark comes out light brown or gold. Too much and you start ablating metal, and the mark turns frosty gray or rough instead of black.

Black marking vs. deep engraving for ATF markings

Under 27 CFR 478.92, required markings such as the serial number must be at least .003" deep, with serial numbers at least 1/16" tall, and depth is measured from the flat surface of the metal. An annealed black mark sits in the surface rather than below it, so it does not meet that depth requirement on its own.

For required markings, use a deep engrave workflow instead. In our shop, an Edge 30W reaches .003" depth on a 1/16"-tall serial number in steel in 20 passes, about 2 minutes. Our post on how deep a fiber laser can engrave covers depth in detail, and the ATF compliance guide covers what has to be marked.

A common approach is to deep engrave the serial and other required markings, then use black marking for cosmetic work like logos and custom text elsewhere on the part.

This is general information, not legal advice. Confirm marking requirements for your specific situation with ATF or a qualified attorney.

Our Edge 50W Presets

These are the LightBurn presets we ship in the settings bundle for black marking and related metal work. Each preset is one pass.

Edge 50W, 220mm lens. Starting points; confirm on a test spot.

A different lens changes spot size and energy density, so expect to adjust speed or interval if you run a 112mm or 300mm lens. Different alloys and surface finishes also respond differently.

How to black mark stainless steel

1. Clean the part

Oil, fingerprints, and cleaning residue change how the surface absorbs heat and can leave blotchy spots. Degrease the area before marking.

2. Focus carefully

Annealing is sensitive to focus because it depends on how concentrated the heat is. Set focus on the actual marking surface, not the fixture. On curved parts like slides, keep the design inside the area where the surface stays close to the focal plane, or use a rotary.

3. Start with the preset, then tune with a test grid

Run a small test square on the same material, ideally a scrap of the same alloy and finish. If the mark is brown or gold, add heat by slowing down slightly or tightening the interval. If it looks frosted or rough, you are removing metal, so speed up or reduce power.

4. Use the image preset for photos and fine art

For grayscale artwork on stainless, our "Image on stainless" preset uses the same power, speed, and frequency as the black mark preset with a slightly wider 0.032 mm interval.

5. Mind heat buildup on thin or small parts

Annealing works by heating the metal. On small or thin parts, heat can build up across a large fill and shift the color. Breaking a large design into sections or letting the part cool between sections helps keep the color even.

A note on corrosion

Annealing changes the surface chemistry of stainless steel at the mark. Industry sources note that heat-affected marks can have reduced corrosion resistance compared with the surrounding metal in harsh environments, and some manufacturers passivate parts after marking. For most firearm cosmetic work this is not a problem, but it is worth knowing for parts that see salt, sweat, or harsh cleaners.

How to black mark brass

Brass is more reflective and conducts heat away faster than stainless, so it needs a lot more energy per spot to darken. That is why our brass preset runs at 100% power with a very tight 0.010 mm interval and crosshatch turned on. The crosshatch fills the area twice in different directions, which evens out the darkening.

Brass jobs in a gun shop include trigger guards, grip caps, small accessories, and personalized pieces. Clean the surface first, since tarnish and lacquer change the result. Some brass parts ship with a clear coat, and that coating can mark unevenly or need removal before you get a consistent black.

What about black on aluminum?

A fiber laser on its own will not turn bare aluminum black the way it does stainless. On anodized aluminum, such as an AR lower, the laser removes the dyed layer and leaves a white or light gray mark (see our AR-15 lower guide). For a true black mark on bare aluminum, apply a laser marking spray and fuse it to the surface with our marking spray preset, then wash off the excess.

Q-switched sources and color on metal

Every Edge Series laser uses a Q-switched source. In our testing, Q-switched lasers produce color on stainless steel and titanium, with fewer color variations than MOPA, and showed a longer focal range than MOPA. For black marking, that longer focal range gives you a bit more forgiveness on parts that are not perfectly flat. Our MOPA vs Q-switched comparison goes deeper.

Frequently Asked Questions

Can I black mark a serial number on a stainless slide?

Not as the only marking. A black annealed mark has essentially no depth, and ATF requires required markings to be at least .003" deep measured from the flat surface. Deep engrave the serial, then use black marking for cosmetic work.

Why is my stainless mark coming out brown instead of black?

The surface is not getting enough heat. Slow down slightly or tighten the line interval in small steps, and double-check focus. Our Edge 50W starting point is 30% power, 4 in/s, 60 kHz, 0.025 mm interval on the 220mm lens.

Will a black mark wear off?

An annealed mark is an oxide layer in the metal, not paint, so it holds up to normal handling and cleaning better than a surface coating. Heavy abrasion or polishing can still remove it because it is so shallow.

Does a 30W fiber laser black mark stainless?

Yes. Black marking is about controlled heat, not raw power, so lower-wattage fiber lasers can black mark stainless with the right speed and interval. Our published presets are dialed in on the Edge 50W, so a 30W will need its own settings tested.

Can I black mark brass with a fiber laser?

Yes, but brass needs much more energy than stainless. Our Edge 50W brass preset runs 100% power, 20 in/s, a 0.010 mm interval, and crosshatch on.

Do I need marking spray for stainless steel?

No. A fiber laser blacks stainless directly through annealing. Marking spray is for metals like bare aluminum that will not darken on their own.

Talk to a Laser Specialist

SA Laser is a veteran-owned company in San Antonio, Texas, serving gun shops since 2012. Every Edge Series fiber laser ships with LightBurn and our settings bundle, including the black mark presets above, so you start from settings that already work instead of from zero. If you want hands-on time dialing in black marks, deep serials, and color on real parts, our 5-day in-person Spark training covers it.

Ready to talk about the right Edge for your shop? Request a quote or call or reach us at (888) 964-3568.