No art is less spontaneous than mine. What I do is the result of reflection and the study of the great masters.

This quote means that the artist speaking does not rely on completely spontaneous (or unplanned) decisions while creating pieces of art. He believes that any art he creates is the result of careful thinking and analysis of the works of famous historical masters of the art. He has likely studied many art pieces and has learned from their techniques and tried to apply them to his own work.