And since coming to the caveau in 1998, the condition of the drawing has not deteriorated any further.
"Volpato's aim wasn't simply financial because, in exchange for agreeing to give the king a discount, he asked to be allowed to become the unpaid curator of drawings in the Royal Library."
Is it really a self-portrait?
Generally dated around 1515, some experts believe the picture corresponds more with Leonardo's style in the 1490s, yet the subject of the drawing is an old man.
Leonardo's Self-Portrait is considered so valuable that it is subject to a state decree of immovability.
"Transportation involved a special 'clima box' able to maintain the same air conditioning systems present here in the caveau," says Saccani. "This 'clima box' was then put inside a case, which was in turn placed in an outer casing, all of which was able to avoid vibration." The package was then driven with an armed escort and constantly monitored using remote technology.
Over the coming weeks, 50 people will be allowed into the Royal Library's caveau every hour from 09:00 to 18:00 to see the self-portrait - the temperature of the vault has been lowered slightly to compensate for the body heat that people will give off.
Subscribe to the BBC News Magazine's email newsletter to get articles sent to your inbox.