working with hard things like slate which is a stone it can be abit hard at times slate will work with out doing anything.
but for best look and clean look you need to clean the slate first and then coat it i use crystal clear mat coat in a spray can.
some i no use the paint on one but i find with the spray you can get a better cover and no runs and it the same all over so when engraving
you can get the same all over and not difrent in other parts with more on. this coat will help it not flake as sometimes when you
engrave slate and you rub clean after it can flake this coat will stop that and any other marks on the slate will hold them in place and you
can not see them. as always with doing any laser work you don’t want something that can make the beam come back on itself this is why I use a mat as it is flat look and if you wanted you can coat over after with a shining coat but only after the engraving never before.