Abstract Original Drawing or Painting authentic Blue Study 15"w x 11"h 1975, vintage

My father, Arthur Jacobson (1924 - 2010), was a noted artist and professor (Arizona State University) with a long career and I have his estate of artworks which includes these oil pastel "sketches" in preparation for larger oil paintings. He handled the medium in a spontaneous and lively way, capturing the clarity and vibrancy of the colors. In his later years, he loved abstract, active shapes and line. This one is an original artwork, untitled (I call it Blue Study) and is watercolor background with chalk pastel drawing lines on top. It's on a heavy, smooth paper, possibly Bristol board. Made in 1975, 11 " h x 15" w. One of a kind, signed and dated by him.
There authentic is some damage due to age to the upper left corner (fold marks) and the upper right corner, fold marks and a small tear.