Jacques Vaucanson by Joseph Boze

Jacques Vaucanson, Oil by Joseph Boze, given by the artist to the 
Académie des sciences in 1784
Paris, Académie des sciences© Académie des sciences – Institut de France

As  far as I can tell, this portrait of Vaucanson in old age by Joseph Boze is the only one for which he ever sat.  There are two copies, one that remained in the family and this one which Boze presented as a gift to the Académie des sciences.

The Dictionary of pastelists has a nice little snippet about how Boze, before he was diverted by Court patronage, hoped that he too might become a great inventor:

"Boze dabbled in inventions, including a machine for unharnessing runaway horses and a hands-free device for turning pages of music, and was a member of the Académie des arts utiles and the Société des inventions et découverts; some of his ideas were praised in a 1780 report to the Académie des sciences by the brilliant Vaucanson - whose portrait Boze exhibited at the Salon de la Correspondance in  December 1782...Boze evidently hoped to make money out of his inventions, but although they met technical requirements they seem not to have been put into production.  However they led to his meeting the comté de Tessé, premier écuyer de la reine who may well have been responsible for his introduction to the court.....

 "Boze" in Neil Jeffares, Dictionary of Pastellists [online version] 
http://www.pastellists.com/Articles/Boze.pdf