I laser etch regularly at work. Most often on hard anodized surfaces and but some not. I use a Panasonic Fiber and Co2 type laser. I have yet to experience an oxidation afterwards. I have some etching that have been done over 5 years ago. I think your going to have a tough time getting the marked surface a dark color. You can achieve a dark mark on stainless, but that is achieved by going slowly and heating up the surface. I have experimented with paint markers and using the laser to control the shapes. Its not a good solution for high volume.