The Search for the Real by Hans Hofmann. I definitely recommend getting your hands on a copy of this book.
“Creation is dominated by three absolutely different factors: first, nature, which affects us by its laws; second, the artist, who creates a spiritual contact with nature and with his materials; and third, the medium of expression through which the artist translates his inner world…The impulse of nature, fused through the personality of the artist by laws arising from the particular nature of the medium, produces the rhythm and personal expression of a work.”
It should be noted that what Hofmann means by “spiritual” should not be confused with the religious use of word. For him the spiritual is an emotional and intellectual synthesis of relationships perceived in nature, rationally, or intuitively.
Art as Illumination 