I'm talking about paintings like this: http://upload.wikimedia.org/wikipedia/commons/6/64/Eos.jpg This doesn't look like Libation, since it's just sort of going everywhere and she's focused on something else. Some sort of one-handed hand washing? But I've seen this before, in a few paintings like this. What is the significance?
In this case, it may well refer to the residence of Eos at either end of the ocean, but a more common use of a pouring jug is as an allegorical image of a river or spring. In many cases, a personification of a river or spring may be shown holding a jug; images of such personifications were especially popular in Renaissance and post-Renaissance art although the motif can be traced back to classical antiquity. A fine early medieval example of this motif can be found in the Neonian Bapistry of Ravenna, which contains a dome mosaic showing the personification of the River Jordan pouring out its waters:
http://upload.wikimedia.org/wikipedia/commons/b/bd/Baptisery_of_Neon_Ceiling_Mosaic.jpg
