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."
Graham Noll of Groveland, who is part of Domoretsky's da Vinci Project Research Group and assisted at Tuesday's presentation, said the messages that the artist embedded in his work were intended for other initiates of the secret societies in which da Vinci was involved.
"The membership of craft and professional associations were given knowledge and ritual to protect, and da Vinci was obliged to pass on the information," Noll said.
Domoretsky said to his knowledge, he is the first to use the mirror imaging to study Da Vinci's work.
Scholars are skeptical of his findings - one critic, for example, questions why da Vinci would conceal the word "Mary" in the folds of the Mona Lisa's clothing when the Italian for Mary is "Maria."
"Anyone who claims to find something new is dismissed by the experts," Domoretsky said. "We are misrepresented because some people don't like what we say."
Domoretsky remains undaunted and continues his research to decode da Vinci's secrets and the meaning of messages he encrypted in his paintings. He plans to hit the road with the show he presented Tuesday in Gloucester.
Domoretsky, who also plans a book, has previously detailed some of his findings on his Web site, www.lionardofromvinci.com. (He believes the artist's real first name was Lionardo, not Leonardo.)
Dana Andrus, master of the Tyrian-Ashler-Acacia Masonic Lodge in Gloucester, said Masons he talked with after the presentation were intrigued by Domoretsky's work.
"I think he is somewhat of a visionary," Andrus said. "He used da Vinci's own insight to look at the paintings. That's someone who has taken a great deal of time and thought, and not listened to the conventional wisdom, and come up with a new idea on how to approach something."