I only learnt this at Dresden Lange & Sohne, when I was literally taught the difference.
Setting relief work apart is the removal of the background, or negative space, leaving the raised design/words.
Of the all ornamental engraving, relief engraving is considered the ultimate treatment.
This time consuming and expensive work is reserved for the finest. The hallmark of quality is a deeply cut background with flat bottom and clean, sharp, sidewalls. A difficult task as good graver control is important.
There's no way to repair a slip without ruining the delicate cuts.
During the outlining process, at least a half-dozen passes, going deeper with each pass is a back breaking work. The particularly close attention to the sidewalls, keeping them sharp and crisp, is an intense eye to hand or machine work. As the background gets deeper, the risk of heel drag increases, especially on inside curves!!!
Imagine: After outlining with the square graver, the background is removed with a GRS/NSK Turbo hand piece. Yes, by hand.
This is a precision air hand piece which operates at around 400,000 RPM greatly speeds up background removal. It utilizes .4 and .5mm carbide ball burs. The thing literally erases metal, in this case, solid gold/platinum. It can be a beast and damage work before you knew what hit it.
Trying to go just a little bit farther with the bur generally results in damaged work.
The background is then stippled with a carbide tool sharpened to a needle point. A heavy foot and stipple deeply at around 4200 strokes per minute. What stippling does is texture the surface.
I think GF does all stippling under the microscope, and faceted tools that have wide shoulders can be difficult to see around.
You can imagine the work done.
It may not be to all a good look, but it is a demonstration of the incredible ability, and the tools, both software and precision laser guided machines they have.
I first went for GF in 2004 because I saw the plates with these words, and I have never seen it on any watch done to this scale and so daring to cut to this depth.