'has'
because of 'some of the painting'.
If so, do you deem the following wrong?'some of' is always followed by either a plural noun or an uncountable noun.
NOT A TEACHER'Some of your article is wrong.'
NOT A TEACHER
To tell you the truth, I'm really surprised and even a bit shocked. Because in every dictionary I've checked so far, about 5 of them, 'some of' is always followed by either a plural noun or an uncountable noun.
Here are some of those dictionaries.
http://www.oxforddictionaries.com/definition/english/some
http://www.learnersdictionary.com/definition/some