Complex sentence: The piece was not like other works executed by Raimondi's School, usually copies of other's preliminary drawings for paintings or frescoes, but a piece that was intentionally created to be distributed through the medium of print.
Split into simpler sentences: The piece was not like other works executed by Raimondi's School, which were usually copies of other artists' preliminary drawings for paintings or frescoes. This piece was intentionally created to be distributed through the medium of print.