[So I’ve been warned below that this isn’t a safe thing to do with the Glowforge, so don’t do as I have done!]
We sometimes joke that my wife isn’t allowed to use the cooking knives that we have - only the plastic one shaped like a crocodile, because she tends to cut herself. To be honest, I can’t remember the last time she actually did cut herself, but I didn’t let that stop me when I engraved these safety messages on one of our knives.
The method I used was to mix isopropanol alcohol with plaster and paint it onto the knife, then simply engrave it at 350/FULL.
It seems quite durable - I can’t scratch it off so it seems the metal has been altered / oxidised.
As for food safety: I don’t rightfully know. “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.” / https://hackaday.com/2014/12/25/laser-etch-stainless-with-only-plaster-alcohol/
Not sure what that says about food safety though. Chromium sulfate - when ingested in large quantities, is not good for you. But the amount formed here - and the amount that would rub off during a cooking episode, should be miniscule. Maybe someone with some chemistry background could help us here?
Is not good for the Glowforge! Free sulfate becomes Sulfuric acid mist and photos have been posted of even tiny amounts of acid destroying a Glowforge after a while. The chrome also though not sure what hexavalent chrome does physically. Even if the formula looks good, that will not be the only result under such conditions.