A laser does two very different things on cotton: cut pieces with clean edges, and above all bleach denim to create patterns — an effect impossible to achieve otherwise at this level of detail.
The faded effect on denim
The principle is not to burn but to remove indigo from the surface of the yarn. At very low power and high speed the laser lightens the fabric without damaging it: you get a photographic gradient, adjustable through power alone.
Always run a test gradient on an offcut of the same garment: two jeans of the same apparent colour react differently depending on dye and washing.
On a garment, keep the fabric taut and the focal distance constant: a single fold creates a darker patch in the middle of the pattern.
Cutting: settings and pitfalls
Cotton cuts at very low power. The edge is not heat-sealed as on synthetics: it will fray, so plan a seam or hem.
Fabric shifts and lifts even more easily than paper. A heavy frame, magnets or temporary adhesive backing are essential for an accurate cut.
Beware of water- or stain-repellent treated fabrics: the treatment is sometimes a fluorinated or chlorinated compound of unknown composition.
Risks and finishing
Cotton is highly flammable and an ember can stay invisible in the weave. Never leave the machine, and let the piece cool outside it before storing.
After marking denim, dry brushing or a cold wash removes dye dust. Avoid tumble-drying a freshly marked piece: heat can blur the edges.
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.