Is "painting" not a countable noun? I thought "a" should be used before "painting" here.

Native speaker’s answer
Rebecca
If you're talking about the actual object, then yes, it is a countable noun! However, here, "painting" is a gerund which refers to the process of making art or painting. Ex: We have a new painting in our living room. Come look at it. => noun Ex: We are going to be painting this afternoon. => gerund