Using mustard to engrave metal?

[beerfaced]

Here is one I did a few years ago:

Metal marking on a knife blade with mustard

After reading a post suggesting mustard could be used to mark metal I gave it a try. I had an old knife kicking around from my sailor days. It served me well (and still does) so I decided to adorn it with the name of the ship we sailed on. I smeared some dijon mustard on it with a Q-tip and used an engraving speed of 1000, power 50. I am totally impressed with the result however a few attempts on different metals did not fair so well. This particular metal obviously reacts well with whatever ch…