Now he's sharing those secrets with the world.
What Domoretsky has found, he says, is a "legacy of hidden messages" carefully concealed in some of the world's most famous paintings and decipherable only to those who know how to read them.
Domoretsky, an Ipswich resident, gave his first public presentation on his research before a roomful of North Shore Masons at their lodge on Eastern Avenue in Gloucester on Tuesday night.
The venue was appropriate because Domoretsky believes the 15th century artist was a Mason who incorporated Masonic symbols, like the compass and square, into his works.
"The best place to hide something is in plain sight," said Domoretsky, who is a Mason himself and works with stone as a self-employed installer of marble and granite countertops.
Domoretsky has had a lifelong interest in da Vinci. But his obsession with the master's secrets was kindled when he came across an image of the "Mona Lisa" on a Web site about the movie "The Da Vinci Code."
He's quick to add, however, that he didn't see the movie until long after he began his research, has never read the book and his work has no connection to the ideas presented by "Code" author Dan Brown.
Domoretsky said da Vinci was a master of optical illusion who created pictures within pictures within pictures - many of them designed to be visible only with the use of mirrors.
In the darkened hall, Domoretsky projected images of two paintings, "Mona Lisa" and "The Virgin and Child with St. Anne and the Infant Saint John the Baptist," as they appear when mirrors are positioned to the right and left of the original artwork.
The resulting twinned images reveal hidden faces and objects and forms that include several chalices and what Domoretsky sees as a high priest of the Knights Templar, a Templar shield and cross and a sarcophagus.
The Knights Templar came into existence after the First Crusade of 1096 to protect European pilgrims en route to sacred sites in Jerusalem. The order was suppressed about 200 years later but, some believe, went underground and survived as a secret society.
Domoretsky believes da Vinci was "heavily involved in Freemasonry and the Knights Templar."