OMTech CO2 Laser Marking Spray

You spray a thin coat, let it dry, and laser your design over it. The coat goes on white and turns black where the beam hits. The excess rinses away and the black mark stays bonded to the metal. OMTech rates it for CO2 lasers of 25W and above, so a 40W K40 or a 45W K40-class machine is comfortably in range.

OMTech lists the kinds of jobs it suits:

• Personalised jewelry and tags
• Custom tumblers and bottles
• Serial numbers and names on tools
• Nameplates and small signs in bare metal

It works on aluminum, stainless steel, brass and many other metals. The formula is cadmium-free, and the same can gives more vivid marks on a fiber laser if you own one alongside the K40.

The mark is permanent in the sense that matters for a product: it does not rinse or rub off like ink, because the coating has fused to the metal. Heavy abrasion wears down any surface mark in the end, so place serial numbers where hands and tools do not grind.

For the full list of what a K40 handles unaided, see which materials a K40 can cut and engrave.

1. Clean the metal. Wipe it with alcohol to remove grease and fingerprints. Oil under the coat shows up as patchy marks.
2. Shake the can well. The agent settles, and an unshaken can sprays thin liquid first.
3. Spray outside the laser. Do it in a ventilated area away from the machine, following the can's label, so overspray does not coat the optics or the gantry.
4. One light pass, then check. You want an even white film with no bare patches and no runs.
5. Let it dry. OMTech gives under five minutes, or about two with a hot air blower.

Drying fully matters. A damp coat smears under air assist and fouls the lens with residue.

For curved items, coat the whole band you plan to engrave, not just the design area. On a rotary, the object turns under the head, and any bare stripe becomes a gap in the mark.

• Tape off areas you want to keep perfectly clean.
• Coat several pieces at once for batch work; the fast drying helps here.
• Keep coated parts dust-free until they go in the machine.

Find your settings with a test grid rather than a guess:

1. Coat a scrap of the same metal you will sell.
2. Engrave a grid of small squares, varying speed along one axis and power along the other.
3. Rinse the scrap and pick the square with the darkest, cleanest mark.
4. Write the winning speed and power on the scrap and keep it by the machine.

Things that change the result:

• Focus. Set it precisely on the metal surface. A millimetre off spreads the heat and greys the mark.
• Line interval. Tighter spacing gives a solid fill; too wide leaves stripes.
• Air assist. Low airflow keeps smoke off the lens without blowing loose coating around.
• Metal type. Stainless, brass and aluminum each shed heat differently, so test each one.

Keep your tube current sensible even when chasing a darker mark. Running a 40W tube hard for long marking jobs shortens its life; a slower pass at moderate current usually marks just as well. The K40 tube and current notes explain the limits.

After marking, rinse the piece under water. The unmarked coating washes off, and the finished item is ready to sell straight away.

• Anodized aluminum marks directly. The CO2 beam removes the dyed layer and leaves a bright mark.
• Painted and powder-coated tumblers and bottles engrave by ablating the coating to reveal the metal beneath.
• Glass takes a frosted mark with no coating.
• Wood, leather and acrylic are the K40's home ground; they never need it.

Where the spray earns its place is bare, uncoated metal: stainless tools, raw aluminum blanks, brass tags. If that is a product you want to sell, one can covers a good run of small parts, since each coat is thin.

Tumblers bring the rotary into play. The OMTech rotary takes objects of 0.8 to 1.6 inches, so slim bottles and tubes fit better than wide drinks tumblers. Coat the full band, set the diameter in software, and test on a scrap first.

Run down this list with the project in mind:

1. Confirm the metal is bare, not coated or anodized.
2. Check your laser is CO2 at 25W or more; a K40 is.
3. Make sure your exhaust vents outdoors.
4. Have 10,600nm glasses for lid-open work, such as the MCWlaser OD5+ pair.

Keep the lens clean, too. A fresh ZnSe focus lens is worth having on the shelf if you mark metal often.