MOPA Color Marking

Colour on stainless and titanium is an oxide layer, not a pigment, so the parameter doing the work is pulse width rather than power. These records, guides, and tools cover the ones people actually chase — gold, red, blue, green, purple — and how to reproduce them once you land one.

Start with a consistent surface and focus

Identify the metal, coating and surface finish before chasing a color. Prepare matching coupons consistently and hold the lens, focus and marking area steady. A recipe from another source or lens is a candidate test, not a guarantee that the same hue will appear.

Test frequency and pulse width deliberately

MOPA color depends on more than power and speed. Use the color-planning and calibration guides to organize changes in frequency, pulse width, hatch spacing and pass count. Label each test cell and keep the remaining controls fixed so a promising color can be traced to its actual settings.

Validate separated artwork on the material

For palette-based artwork, inspect each color region and the layer order after import. Mark a small representative sample, including fine boundaries between colors, before the finished part. Record the accepted physical result with its settings; screen colors are a planning aid rather than a prediction of the metal.

Why colour needs a MOPA source

The colour on stainless is thin-film interference: the laser grows a transparent oxide layer, and its thickness decides the hue. A standard Q-switched fiber has a fixed pulse width, so it mostly makes black or grey marks. A MOPA source lets you set pulse width on its own and run the high frequencies colour needs. Thin oxide reads as straw and gold, thicker layers move through violet and blue to teal and green.

Read a colour recipe as a direction, not a number

The starting recipes for stainless 304 run from gold at long pulses and low frequency (about 180 ns at 300 kHz, 1000 mm/s, 18%) to green at short pulses and high frequency (about 42 ns at 1500 kHz, 400 mm/s, 36%). Learn the direction rather than the values: more heat per area grows thicker oxide. Your source, lens, field size and metal batch move every number, so bracket around the recipe on your own machine.

Set hatch, direction and focus before chasing hue

Use a tight line spacing (about 0.002 to 0.005 mm) and single-direction, parallel hatching: crossing the lines at 90 degrees can cancel or blend the colour. A little defocus widens the beam and softens the oxide toward pastel tones, while tight focus drives deeper, darker marks; blues and violets often reproduce best around 1 mm of defocus. Change one of these at a time.

Build a colour grid you can read later

The MOPA Color Predictor in the Laser Lab takes your wattage and lens and suggests a recipe with its line spacing and defocus. Bracket it with a test grid: the free EZCAD test card writes a DXF with every cell on its own pen and a CSV of each pen speed, power, frequency and pulse width, and the MOPA Colour Sweep writes a native .xcs card for the xTool F2 Ultra. Label the plate before you mark it.

Clean and handle the blank like it matters

Wipe stainless with isopropyl alcohol just before marking and handle it with lint-free gloves: fingerprints and oil oxidise unevenly and muddy the colour. Keep coupons from the same batch and finish as the finished part. A brushed and a polished surface of the same alloy can give different hues from the same recipe.

Know what a MOPA will not colour

Oxide colours work on metals that grow a clear oxide, mainly stainless steel and titanium. On polymer, such as a magazine body, a fiber or MOPA laser bleaches or foams the plastic instead, so every mark is lighter than the part. PMAG TONES in the Fabricator keeps a design to the tones a laser can make on polymer and exports one layer per tone, with a free test grid for a scrap part.