If that's the effect you want, it's fine! It's not a lithophane but it does give quite a good 3D effect. However, the finish you are getting from the tool really isn't very good and I think that you need to look at the tool you are using, speeds/feeds, stepover, etc. Can you say a bit more about the machine you are using and the settings, and maybe you will get some suggestions on how to improve finish? At the moment, you will need a lot of hand-finishing before you can think of what varnish/oil/wax would work best.