The experience of painting portrait studies from art history — copying masters' portrait work specifically — has taught me things that no other study approach has.

What master copy portraits reveal: the specific decisions about how much softness to give edges, how saturated to make skin tones, how to handle the transition from hair to forehead. These are all judgment calls that the master made and you're reverse-engineering.

The specific study that changed me most: copying a Rembrandt self-portrait. His shadow transitions are almost completely invisible on close inspection — there are no sharp edges anywhere except in the focal point (the eye closest to the viewer). The painting is built from gradations so subtle they register as form rather than paint. Matching this forced me to develop a patience with gradual transitions I hadn't had before.

The limitation of master copies: you develop the ability to replicate the specific artist's judgment, not necessarily to develop your own. Alternate master copy practice with imagination work to ensure the learned judgment transfers.