If you’re looking to have the engraved/rastered area silver, and want wood as your material, then deep engrave, spray paint in very light coats and run the board over a sander to clean up any bleed.
If you want a silver surface, with “charred” engrave, look at this laser foil technique. I’ve posted it before, but you may not have seen it.
Edit: I may not have linked this in the most efficient way, click on the heading to go to the full post with a video on the method.