Two ways to a negative
If your design is an image, invert it: what was black becomes white and is no longer engraved, and the former white background is now engraved. If your design is vector artwork, draw a filled rectangle or shape behind the text and subtract the letters from it, so the fill covers everything except the letters. Both give raised text on an engraved field.
- Image → invert
- Vector → fill with the text cut out
- Result: raised text, engraved field