Here's a site that shows very simple line drawings of shapes of seventeen pottery vessels that would have been commonly seen in ancient Greece:

http://www.artfromgreece.com/vshapes.html

And 'krater' (or 'mixing bowl' as Flagles and others like to call it) is defined here:

Ancient Greeks had usually drunk wine mixed with water. "Krater" is a mixing bowl and the name is from the word "Kerannmi" means to mix.

http://www.officenet.co.jp/~yoji/vase/s_mix.html#skyphos_krater

Another Edit or Addition:


Just as Faldage wrote above, there's this mentioning of the yeast and alcohol content of wine:

"Unmixed wine tended to be strong, with an alcohol content as much as 15 or 16 percent (at which point the yeast is killed by the alcohol it produces) and was considered unhealthy by the ancient Greeks, who customarily diluted it with three or four parts of water. The wine always was added to the water, usually in a large mixing bowl or crater (krater), such as illustrated here"

http://itsa.ucsf.edu/~snlrc/encyclopaedia_romana/greece/hetairai/tondo.html