Marking spray is the way to mark bare metal without a fibre source: a thin coating on the part vitrifies under the beam and bonds permanently to the metal. A CO2 or a diode is then enough.
Settings: what really matters
The coating must be thin and even: two crossed spray passes, fully dried, no runs. Too thick and it flakes instead of bonding; too thin and the mark has gaps.
The classic setting is high power at moderate speed, single pass. Adhesion comes from contact between the product and the heated metal: too fast and nothing takes.
The result is matt black. It lacks the fineness of true fibre marking, but it is perfectly legible and permanent.
Risks and finishing
The product comes as an aerosol: follow the maker's instructions, ventilate the room and wear a mask while spraying, outside the machine.
Metal still reflects the beam even when coated: lid closed and goggles matched to your source.
After marking, rinse the part with water: unfixed product washes off and only the bonded mark remains. That is also how you confirm the setting worked.
Every figure on LaserSettings comes with the machine, the laser source, the material and the thickness it was tested on. A setting published for a 10 W diode says nothing about a 40 W CO2, and a setting for 3 mm says nothing about 6 mm: check those four things before you copy any number.
Settings are confirmed or disputed by the members who reproduce them, so reliability comes from cross-checking rather than popularity. Photos of the result — cut edges, engraving shades, scorching — tell you more than a single number found on a forum.
Whatever the material, treat a published setting as a starting point: run a small power/speed test grid on an offcut, clean the lens, redo the focus, work with fume extraction and air assist, wear glasses rated for your wavelength and never leave the machine unattended.