Adriaen de Vries most often used a technique called "direct lost-wax casting." During the casting process, the wax of the original wax-and-clay model melts out, or is "lost," hence the technique's name. Because the model disappears, each bronze cast produced is a unique original. If the casting fails, the sculptor must begin again. Thus, only the most confident sculptors worked in this method.
Learn more about de Vries's traditional direct lost-wax approach: http://bit.ly/z4itlA
Read a biography of Adrien de Vries from the Getty Museum: http://bit.ly/ApZgky
Description of Juggling Man by Adrien de Vries: http://bit.ly/wpgHM9