I finally cracked the code for vibrant, repeatable colors on Titanium (No ink/chemicals). Here is the physics and parameter breakdown.
I see a lot of folks here struggling to get actual colors on titanium and stainless steel. Usually, the result is just a muddy dark brown or a faint yellow that wipes off. I spend a lot of time testing material limits in our application lab, so I wanted to share the actual physics of how to "paint" with a laser and stop burning your metals.
The Physics (Why you aren't actually using "color")
When we mark colors, we aren't depositing pigment. We are creating what's called a LIPSS (Laser-Induced Periodic Surface Structure) or controlled oxidation.
You are basically using the laser to instantly grow a transparent oxide film on the titanium. The color you see is just light refracting through that film (like a soap bubble).
Why your standard Q-Switched laser is struggling:
If you have a standard 20W or 30W Raycus/Max source, your pulse width is fixed (usually around 100-120ns). It delivers heat like a sledgehammer. It blasts through the oxide layer and just carbonizes/burns the metal.
The Parameter Secret (MOPA):
To get those bright blues and magentas, you need surgical control over the heat. You need a MOPA source where you can drop the Pulse Width down independently.
Here is a baseline recipe I used for a Deep Sapphire Blue on Grade 5 Titanium:
Speed: 2000mm/s
Power: 85%
Frequency: 150 kHz (Notice how high this is! We want gentle, overlapping heat)
Pulse Width: 4 ns (Extremely short bursts)
Line Spacing: 0.002 mm
Focus: +1mm Out of Focus (Crucial: defocus slightly to spread the photon energy and avoid ablation)
The Gear:
For transparency, I ran these specific tests on our shop's HeatSign 60W MOPA workstation, but this theory applies to most high-end MOPA sources if you dial in the frequency-to-pulse-width ratio correctly. The stability of your galvo head also plays a huge part in keeping the colors uniform across a larger fill area.
If anyone is trying to dial in a specific color on their setup, drop your parameters below and I’ll try to help you troubleshoot why it's burning.