Daniel,
Here is one of the mild steel sample plates. I did not finish it. That's a good thing because it allows you to see the technique.
Notice how only the outline and main low spots are heavily and quickly cut out with gravers. A square is used for the outline and flat areas and a round is used for the rounded low spots.
Then punches are used to chase, mold and detail the shapes by moving the metal around.
This would still need to be scraped and stoned or burnished to a final finish.
I first became interested int his technique when I saw a practice plate that Sam Alfano had. I was fortunate enough to get to inspect it first hand at last years engraving in and picks Sam's brain a bit about how he did it. I pretty much took the basic concepts and ran with it.
Ray