This seems like a good approach for projects from life when you have limited time. The effects were easy to get. From the beginning there is a complex silver and gold glow that just seems to appear. Getting close to the canvas, you can see how much the visual effect relies on the warm underpainting which can be a drawback. The half-tones may have less body than other methods. Some of Rubens paintings look like they were left like this (it is a very loose, spontaneous look). Maybe this is what his first painting looked like. I followed the approach suggested in Max Doerner's The Materials of The Artist and Their Use In Painting. This was an experiment and I am not a Rubens Expert-FYI...