Paul Gillis is an artist's artist who toils away in his studio, creating quirky, cartoonish paintings and watercolors — but rarely exhibits them. Realizing that, Simon Zalkind, one of Denver's most gifted curators, mounted a show devoted to pieces that Gillis had done over the last dozen years, almost none of which had been displayed before. Although the works are nominally narrative, it's hard to say just what story Gillis is telling: His pictures include robots, animals and vessels of various types, as well as writings in imaginary languages, all of it set in weird, surrealistic settings that look simultaneously ancient and futuristic. His cryptic work was a fitting choice for the Singer, long a force in the Denver art world, but now facing an uncertain future at the Jewish Community Center.