Marie Antoinette's gold Breguet pocket watch, ca. 1827. It took 44 years to complete after it was first commissioned in 1793. Marie Antoinette never saw the watch through to its completion, as she was sent to the guillotine 10 years before its completion. It is referred to as the Queen/Mona Lisa of watches.
Paint Thinner: You can go all out and get the Speedball Art Products Mona Lisa 1-Gallon Odorless Paint Thinner. The lack of door helps work in smaller studios and it keeps well for a long time, if well capped.