What comes to mind for the use of fissures in the UK covers , framing motifs in rectangles /trapezoidal enclosures , separtes motifs , joins one or more motifs , provides an edge that curtails a motif (odd because the fissure was almost certainly there first but the engraver allowed it to transform the shape of the motif rather than incorporate it , the same effect being found at the edge of rocks where it's almost as if the motif had been cut ). Man made grooves have the same uses. All types and of markings use them from simple cups to ornate .
It may be possible to exclude some examples of