So I had a couple rocks custom cut, each are 12" X 3" X 1" and come with slurry stones.

Top one is a Welsh slate at 15+K Thuringan (correct me if I have the wrong name)
And the second is a purple LLYN MELYNLLYN at +- 12K

I was wondering what is the best way to treat the surface? There are a few deep scratches in the face, would they cause issues? Is it possible to wreck the surface trying to smooth things out?

I have read a couple posts on the slates, but all its done is made me scratch my head. If someone can make an educated guesstimation from the pics and provide an opinion on how to finish the surface, I would appreciate it.

Now, I need to learn to use them correctly! lol!!

Here they are wet.