So I just found these awesome flat smooth coasters and did a test on them using @Jules settings found here: Settings for Engraving on Slate - #3 by cynd11
Turned out great, here’s the video of it:
Here’s some photos, original is on left and shellac is on the right:
Excellent results!
Looks fantastic! That shellac makes a real difference! 
Yea, I think it depends on the lighting as well, cuz in some lighting the original looks better. So either one is great to me.
Both look great. Bonus is shellac is food safe and OK to use if the slate will be used as a food tray.
Seeing a lot of slate this morning … love the turnout with the shellac.
