Many hobbyists and hackerspaces have the $500 Chinese 40W lasercutters which most of us know are about as successful at etching metals as a featherduster is at drilling. [Frankie] and [Bryan] have figured out a way to use the laser to chemically activate an etching process. See experiment part 2 as well.
First, to be clear, they are using a quality 40W Epilog Zing, not the cheap one, but40W is40W. They mixed the plaster (calcium sulfate) with Isopropyl until it resembled white ketchup. After either thinly painting or airbrushing the material onto the stainless surface (both worked), the mixture is dried with a heatgun then put into the laser. 100% power and 5% speed was what worked for them.
The result was an engrave with a noticeable bite. Something they claim had no effect at all without the mixture.
Stainless steel is an alloy of iron and some chromium – not the same as chrome-plated steel. [Frankie]’s explanation of the chemistry is that the surface layer of the stainless is a transparent chromium oxide. With the heat of the laser, the calcium and chromium swap dance partners. Calcium takes the oxygen and chromium takes the sulfate. The calcium oxide washes off but the chromium sulfate causes the etch.
Next time you’re at your local space, give this a try.