In my case the artwork was SVG vectors. I had to isolate the sets of closed vectors and then increase or decrease their size proportionally as individual shapes.
In some cases I did have to node edit the curves as simply resizing enlarged areas inappropriately. It pays to learn how to massage your artworks with various tools like Inkscape, etc.
i would like to use Rust-oleum products… but here in Europe those cans can’t arrive. I asked to an online seller, Jbtools if i remember well, that told me that aerosol cans can’t be sold outside America.
All you need to do to increase the image cut is to use a single coat of clear spray, Tremclad, Varathane, MinWax, Krylon etc. I prefer Satin finish. This will give you more contrasting image. If you add a second clear coat after burning, that helps to seal the material but it also reduces the image contrast a wee bit.
I will add I seal with lacquer clear satin or semi gloss. Dries real quick. Works well for me but that is just my method….others may prefer different methods.
I dont think you need to go as fine as 600. Anything you do will leave you with a grey surface, so you dont likely need much finer than 220 or 320. After that give it a coat of clear stain finish from Tremclad or Varathane, I think that will bring it back to black for you, plus the clear coat gives you a higher contrast when burning anyway, I always use do that. Clear coat after burning does remove a bit of the contrast you just gained, so it depends on what use the tile is being put to as to whether or not you want a second clear coat. I find that high gloss takes away from the impact of the burn, so satin is my preferred finish. This info was posted on the ortur user group by another fellow but I never followed it up. I do have some tiles that could be re-used I just havent got to it yet.