Engraving is usually the process of forming an image by removing some of the surface of a material.
What are some of the common methods?
A laser engraver uses heat to leave an image.
A rotary engraver typically uses a rotating cutter which works a lot like a carpenter’s router bit.
Diamond drag uses a diamond stylus which is drug over the surface to form very fine scratches in the surface.
Chemical etching may be used to dissolve some of the surface.
Sandblasting erodes the surface in a way similar to sandpaper.
Sometimes an image is made by adding material to the surface of the object being done. This approach includes pad printing, sublimation printing, silk screening, direct colour printing and in the case of stainless steel, Cerdec.
It probably comes as no surprise that every one of these processes work very well on some materials and very poorly (or not at all) on others.