Is it painting or paintings when we refer to it as a form of art?

There are two definitions of the word painting in the Cambrige Online Dictionary, The first is

a picture made using paint

which has as one of its examples

an exhibition of 19th-century French painting

and the second is

the skill or activity of making a picture or putting paint on a wall

With an example

We were taught painting and drawing at art college

When we speak of the art works consisting of painted images produced by an artist who worked or works in multiple media (Leonardo da Vinci for example) we can refer to it either as "the paintings of Leonardo" or "the painting of Leonardo". In the first case we are talking about the collection of images but in the second we are talking about the painted images as a whole which can also be considered as the product of the activity (like the "we were taught painting" example above.

When we speak of the body of work of an artist who worked almost exclusively in paint (Van Gough for example) we almost always use the singular form which refers to the body of work as a whole or to the activity as a whole by saying "The painting of Van Gough"

The only problem with doing this is that it can be ambiguous with the alternative meaning of "the painting which has the artist as a subject" For instance "The paining of Van Gough with his ear bandaged"

In conclusion it is possible to use either the singular or the plural depending on the context. For instance we can say "the majority of the paintings of Van Gough were inherited and later sold by his brother Theo" because we are talking about the artifacts and not about the body of work as a conceptual whole.