I noticed that it's common to use Fleck with auf rather than an. For example Es gibt einen Fleck auf Ihrem Hemd. ("There is a stain on your shirt.") My understanding is ''auf'' means "on top of" while ''an'' means "attached to", "leaning on", "hanging on/from". So it seems odd that auf rather than an would be the preferred preposition here. Is this just a random exception or is this part of a more general pattern? Apparently with Farbe the preferred preposition is an, as in Es gibt Farbe an der Wand. ("There is paint on the wall.") But there are exceptions with this: Es gibt Farbe auf der Palette. (There is paint on the palette.") I suppose it's because a palette can be held horizontally.
This follows straight from the progressive aspect, sich etwas über das Hemd schütten. Consequently, the stain is upon the chemise, so to speak, not onto. (PS: this should be logical, that fluids come from above, because they generally flow down wards).
The preposition is occasionally allowable, per chance, if the stain is superficial, so you might have Ketchup an der Backe, but this has never been applicable with cotton wool to my knowledge. Further, we'd more likely say im Gesicht, not an, showing that it depends on the location and how it combines.
Imaginably, English has generalized this to on under inuence of French en, which I understand combines both n-prepositions, in turn under the influence of Frankish, though the severely reduced á might also have played a role.
I'm somehwat surprised, that DWDS does not offer a dedicated meaning for an as well as auf.
No, I don't think is has to do with the orientation of the stained surface. Neither would I translate auf with on top of but rather prefer upon.
Numerous other examples exists:
- Auf dem Bildschirm...
- Auf dem Gemälde...
- Auf dem Plakat...
- Auf dem Foto...
I would mostly use auf, when the "carrier" is used as a reference and offers the surface exhibiting something.
Counter-examples using am exist, however, but I don't see a clear and easy rule here:
- Ich habe einen blauen Fleck am Schienbein.
- Am Kotflügel ist ein Kratzer.
It is as it is :-)
Just like a stain is upon but a writing on the wall.
Ein Fleck ist auf, ein Knopf an der Bluse, eine Nudel ist im Gesicht.
But I would translate "auf" not only with "on top of", that'll be more like "über". I don't think there are general equivalents either way in both languages for these prepositions/adverbs/prefixes.