I feel that drawing from museum busts is a great way to practice drawing portraits. So I went to the Walter's Museum in Baltimore with a sketchbook and mechanical pencil and started to draw the ancient greek and roman statues. There are several advantages to drawing from ancient busts. The sculptures are usually very realistic in terms of proportions and the white marble actually helps in seeing the facial structure as volumes rather than as hair, eye, nose etc... You can also draw it from many angles, unlike drawing from a photograph. And of course, unlike a real human, it won't move. So its a great way to start and build speed before tackling live subjects.
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From @siloe