A fundamental assumption in art therapy is that the art work is related to the artist and her/his inner representations. This idea involves diverse differential psychological and clinical constructs. Quantitatively this hypothesis has barely been tested yet, because suitable empirical instruments are rare. This is where the rating instrument for two-dimensional pictorial works (RizbA) contributes. The test measures the construct pictorial expression and includes aspects of a classical picture analysis like representation, color, shape, space, motion, composition and expression, which in combination create the overall construct. Test construction is empirically-based and led by theories of art therapy and art as well as existing instruments of picture analysis. For empirical examination two studies were conducted so far. Another study using a test-retest design and a representative sample is still running. For the present two-dimensional pictorial works created by adult amateurs serve as material and are analyzed by experts using the rating instrument. The preliminary version includes 26 items. Its ability for differentiation between pictorial works ranges between .897 (T1) and .766 (T2), its inter-rater reliability between .525 (T1) and .917 (T2). Test-retest reliability is .919. Principal component analyses suggest a four-factors solution, which in large part is consistent across studies. As a reliable objective measurement RizbA opens new perspectives in practice as well as in fundamental and applied research in art therapy, art science and psychology.