# MOPA colour on polished stainless: notes and RGB test plan (2026-10-15)
Machine: ComMarker B4 60 W MOPA, 110 mm lens, LightBurn 1.7. Material: 24.5 mm polished stainless coins.

## Colour model
Oxide-film interference; thickness sets colour (straw/gold, brown, purple, blue, then 2nd order pale gold, red/magenta, green, then grey/black). Main control: energy density E = W/(speed x interval) J/mm², W = power% x 60 W; crosshatch and passes multiply dose. Pulse width and frequency set pulse energy (W/f) and peak power; longer pulses run warmer. High pulse energy or slow high E causes sparks/burning. Large fills run hotter than small test cells.

## Verified by eye
- Purple R1-0106: 15%, 567 mm/s, 280 kHz, 80 ns, 0.004, crosshatch x2 (E≈3.97)
- Deep blue R1-0805: 7.5%, 700, 119 kHz, 60 ns, 0.005, x2 (E≈1.29)
- Blue R1-0904: 15%, 1200, 230 kHz, 60 ns, 0.005, x2 (E≈1.50)
- HD fill black: 14 purple-setting layers at rotating angles + 2 blue facet layers; glossy black, ~130 min per coin.

## Lessons 2026-10-15
- Hard black (20%, 567 mm/s) sparked and burned on a colour-field coin. For black fields use 4 passes of the HD-black purple setting at 0/45/90/135 (~14 min per coin).
- Gold R1-1202 was output-off in that burn and never fired, so gold is **UNTESTED** (it did not fail to show).

## Verified by Hank 2026-10-15 on large field wedges (24.5mm polished SS)
- Lavender/light purple: 15%, 567 mm/s, 280 kHz, 80 ns, 0.004, crosshatch x2
- Slate blue-grey: 7.5%, 700 mm/s, 119 kHz, 60 ns, 0.005, x2
- Pale grey-green/silver: 15%, 1200 mm/s, 230 kHz, 60 ns, 0.005, x2
- Brown-black with sparks/burned edges: 20%, 567, 280 kHz, 80 ns, 0.004 x2, and 30%, 300, 50 kHz, 200 ns, 0.01 x2. Avoid these on fields.

Note: big areas came out much paler than the small test cells (large fills run hotter). The purple vs slate-blue mapping could be swapped (medium-low confidence).

## Published starting points (other machines; scale before use)
- Red: 45%, 1000 mm/s, 60 ns, 400 kHz, 0.02 (30 W JPT, 110 mm) hobbyistlaser.com/blog/color-marking-stainless-mopa-settings
- Gold: 35%, 1000, 80 ns, 800 kHz, 0.02 (same)
- Blue: 40%, 1500, 100 ns, 600 kHz, 0.02 (same)
- Red: 27%, 800, 300 kHz, 60 ns, 0.003 (60 W JPT, 210 mm) forum.lightburnsoftware.com/t/experiences-with-color-marking/125488
- Green: 200 ns, 70 kHz, 25%, 600 mm/s (60 W JPT) anypowerrun.com/post/detail/1313/
- Gold bands 140-200 ns 200-260 kHz; green 420-500 ns 40-60 kHz (20 W) stylecnc.com/blog/mopa-color-laser-engraving-settings-stainless-steel.html
- Line interval matters more than speed/power; red and green are hardest on 110 mm: forum.lightburnsoftware.com/t/mopa-colours-hunting-for-a-good-red-and-green-on-brushed-stainless/136015
- Power % scales with wattage; ns, kHz and speed don't: mopacolorstudio.com/utilities/mopa-color-reference-chart.html

Scaling: halve power % of a 30 W recipe for 60 W; 110 mm lens has a smaller spot, so start about x0.8 and sweep.

## RGB calibration test (8 faces = 4 coins front and back, 26 labelled 2.2 mm cells each, power 25% or less)
F1 E sweep 0.5-16, 80 ns, 1 pass. F2 same, 2 passes, E 0.5-8. F3 E 0.5-16, 60 ns, 230 kHz. F4 forum-red geometry, E 2.5-16, 1 and 2 passes. F5 pulse width 2-200 ns. F6 frequency 30-800 kHz at 60/200 ns. F7 200/350/500 ns warm/gold plus published gold and green. F8 verified colours at x0.7/1/1.4/2 plus published reds. About 21 min total. Results get photographed under fixed white light and fitted to colour = f(dose, ns, f).