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How to engrave metal with a laser: bare, anodised, coated

Which lasers engrave metal: why CO2 and diode lasers need marking spray on bare aluminium, why anodised and coated metal mark directly, and what fibre adds.

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Whether a hobby laser can engrave a piece of metal depends on the surface more than the metal. Anodised aluminium and powder-coated metal mark directly with a CO2 or a diode laser, because the beam works on the coating. Bare metal, bare aluminium included, mostly reflects those beams: it needs a marking spray that the laser bonds to the surface, or a fibre or infrared laser, which metal absorbs. Hobby CO2 and diode lasers are not the tool for cutting a groove into bare metal.

What works on what

SurfaceCO2 laserBlue diode laserFibre or 1064 nm infrared laser
Anodised aluminiumMarks directlyMarks directlyMarks directly
Powder-coated metalMarks directlyMarks directlyMarks directly
Bare aluminiumOnly with marking sprayOnly with marking sprayMarks directly
Other bare metal, such as stainless steel or titaniumWith marking sprayCheck your maker’s guidanceMarks directly
Copper, chrome and other metal that reflects the beamNot laser-compatible in Glowforge’s CO2 machinesCheck your maker’s guidanceCheck your maker’s guidance

The sources for each row are in the sections below. A table like this cannot promise a result on your machine, so test on a spare tag or the back of the piece first.

Why bare metal is hard

Epilog, which makes both kinds of laser, puts it in one sentence: “bare metals reflect the wavelength of a CO2 laser, meaning direct marking typically requires a fiber laser source.” Epilog gives the wavelength of its CO2 lasers as 10.6 microns and of its fibre lasers as 1064 nanometres, and says its fibre machines are “capable of permanently marking nearly all types of bare metal”.

Blue diode lasers, which xTool puts at 450 nm, are in the same position as CO2 for bare aluminium. xTool’s guide: “if you engrave bare aluminum using a CO2 laser or blue light diode laser engraver, you need to apply a coating of metal marking spray to the surface before engraving it.”

Reflection is also a hazard. Glowforge says of its CO2 machines that “materials that reflect laser light are not laser-compatible”: copper and chrome “can reflect the infrared laser light, which can be hazardous to people and damage your Glowforge”. Follow your own machine’s manual on what metal may go in, and keep the enclosure closed. Galvanised metal must not be lasered at all: Glowforge says it “can release hazardous gases”.

Anodised aluminium

Anodising grows a hard oxide layer out of the aluminium itself, and the layer can be dyed almost any colour. Epilog describes what the laser does to it: the beam “bleaches” the surface, which gives “a bright contrast”. On a black tag the mark is light.

  • It works with CO2, diode and fibre lasers. xTool explains that the oxide layer absorbs wavelengths that bare aluminium reflects. Trotec says 30 watts of laser power is enough.
  • It needs no spray or other consumable.
  • It does not cut into the metal. Glowforge notes that the process “discolors the metal but does not engrave it away, so the surface still feels smooth to the touch”. Epilog adds that it does not harm the protective layer.
  • It holds fine detail. Trotec says “almost photographic qualities can be achieved”.

For a photo, the colour of the blank decides whether to invert it. LightBurn’s documentation gives the rule: invert an image for “slate or another material whose original surface is darker than the mark your laser will make on it”. Black anodised aluminium is such a material, since Epilog and Trotec both describe the mark as bright or light, so a photo for a black or dark blank is inverted first, and the laser converter has an Invert switch for this. Epilog’s photo guide says that anodised aluminium “typically” does not require inversion, without naming a colour, and adds that “testing is always recommended”. If your blank is pale, or you are not sure which way the mark will go, engrave a small piece of the photo both ways before the real one. Dithering for laser engraving has notes on dot patterns for metal.

Anodised blanks are the easy way into metal: Glowforge’s page links to owners’ anodised business cards and keychains. Check that a blank is described as anodised before you buy it.

Powder-coated metal

Here the laser works on the coating, not the metal. xTool lists powder-coated aluminium as engravable by CO2, diode and fibre lasers with “no need for any pretreatment”, and Epilog says CO2 machines “directly mark” coated metals such as powder-coated stainless steel.

The caution is the coating itself, and it goes for painted metal too. Glowforge’s rule applies: coatings, dyes and paints “may not be laser-compatible”, and if you are not sure what a coating is, do not put it in.

Bare metal with marking spray

Marking spray, also called marking compound, is how a CO2 or diode laser puts a permanent mark on bare metal. Epilog describes the result as “a permanent black, silver, or sparkle-type mark”. Epilog names CerMark, Enduramark and LaserBond as common products. Its description of the process:

  1. Apply the marking solution.
  2. Allow it to dry.
  3. Engrave as normal. “The heat from the laser bonds the solution to the metal.”

Follow the instructions on the can for preparing the metal, for removing the leftover coating and for ventilation.

What you get is a mark on the metal, not a groove in it. Epilog: “you’re creating a surface mark, rather than etching into the metal itself”, and the result is “a durable and permanent raised mark”. Epilog gives titanium and nickel plating as examples of metals treated this way, and stainless steel tumblers as a typical product. Trotec says the same of aluminium: with a marking spray “you can also engrave with a CO2 laser”.

Settings differ for every spray, metal and machine. Start from the spray maker’s figures for your type of laser, and run a small grid of power and speed on a spare piece. Judge the squares after cleaning off the leftover coating: you want the one that leaves an even, lasting mark.

Fibre and infrared lasers

A fibre laser is the tool made for metal. It marks bare aluminium, steel, brass, titanium and the rest with no preparation, and it can engrave to a real depth. Some hobby machines, xTool’s among them, pair a blue diode with a 1064 nm infrared laser for this reason. xTool describes such infrared lasers as suited to metals and plastics, and notes that the blue beam suits wood and leather. If metal is most of what you want to do, that is the kind of machine to look at, and its maker’s material list is the one to trust.

Infrared light cannot be seen: Glowforge says of its own infrared laser that the light “is invisible”, and LightBurn’s safety page warns of “light that may not be visible”. The rules on enclosure and eye protection in laser engraving tips apply in full.

Engraving metal without a laser

A laser is not the only way to mark metal at home, and for a real groove in bare metal a hobby CO2 or diode laser is the wrong tool. Glowforge says of its CO2 machines that “soft metals such as gold, silver, brass, copper don’t cut or engrave well”, and points to fibre lasers and small milling machines.

A Cricut Maker with the Engraving Tip cuts a fine groove into thin aluminium, anodised aluminium, brass, bronze, copper and stainless steel; the Cricut engraving tool covers it. Hand tools are outside this guide, which is about lasers.

Questions

Can I engrave bare aluminium with a diode laser? Not directly, according to xTool. With marking spray, yes. A diode laser marks anodised aluminium directly.

Will the laser cut the metal? Treat it as no for hobby CO2 and diode lasers. Epilog says its own machines, CO2 lasers of 30 to 120 watts and fibre lasers of 10 to 50 watts, “are not ideally suited for metal-cutting applications”, though its fibre lasers have cut thin foils.

Is a marking-spray mark permanent? Epilog calls it durable and permanent. It is a bonded layer on the surface, not a groove.

Why did my anodised tag barely mark? Run a small test grid of power and speed on a spare, and check with the supplier that the blank is anodised.

Sources