"...The purpose of the German Schlager duels was to create fancy scars, aka Heidelberg scars, so that the German "gentlemen" could show off visible evidence of their bravery. The last six inches or so of the blade toward the tip were sharpened. No mask was worn and, when skin was broken, an irritant was rubbed into the cut to make a keloid type scar..."
I thought Heidelberg was the one place that they were used stabbing weapons rather than the Schlager (something to do with facial scars on theology students) - I'm sure I'll be corrected on this point.
"...No mask was worn..."
I believe there was, however, a modified set of goggles with a 'nasal' protecting the eyes and length of the nose (presumably 'out of play' areas).

Of formal duels, in the British Army of the Penninsula War, Wellington had to issue an order forbidding duels among his officers.

W