My ISTJ is artistic too, in the sense of having a very good ear for music and having a very particular visual aesthetic taste for things like form and color. But like with my ESFJ ex, the form of being artistic seems more inclined to collection and selection and taste rather than raw manipulation of materials. My ESFJ ex collects films from all over the world, is totally a film snob, keeps them perfectly organized, and has a similarly heightened sense of form and color, though it's different in the specifics from the ISTJs. (Si is personal.)
My ISTJ grandfather was not "artistic" at all, though, unless you count the fact that he was a well-groomed snazzy dresser and he liked picking out pretty dresses for his wife and daughters and granddaughters...I would call him the more traditional image of a very practical ISTJ rather than a real aesthete or artist, though he liked people to dress nicely. He also used to buy me these collector's item porcelain dolls. Selecting and collecting and taste , again, rather than raw manipulation of artistic materials.
Not to say that there aren't SJ painters and writers, because there are of course. William Wordsworth was an ISFJ poet.
I still think Melancholic makes more sense for Si types in general, including INFPs with their tert Si.
EDIT: Maybe that's it! Maybe it's Si/Fi or Fi/Si...hmmm...