(CNN) -- Peter Hohenstatt was skeptical at first, especially when he learned the drawing dated to about 1500.
The sketch was absolutely Leonardesque, the University of Parma art historian thought, but it was probably the product of one of the master's students, imitators or admirers. When a technical exam showed the drawing originated closer to 1473, his skepticism waned.
The reason? Leonardo da Vinci was an apprentice until the late 1470s. He didn't have any students, imitators or admirers of his own yet.
I can't be sure it's a Leonardo drawing, not scientifically or any other way, said Hohenstatt, but I'm highly convinced that we have here one of the first drawings. I'm quite convinced it's one of his first portrait sketches.
Hohenstatt isn't alone. Da Vinci expert Luigi Capasso told CNN there is a very high possibility that this sketch is by Leonardo da Vinci.
The object of their fascination is titled simply, red pencil drawing of a profile of a man's head looking to the left. It was found about 70 years ago tucked into a book -- and like many objects of artistic intrigue, it has a long and twisting story, regardless of whether it's the product of the Renaissance master.
The two men's convictions are based on artistic similarities to other da Vinci works as well as the makeup of the sketch's paper, which they say is similar to the paper da Vinci used in other sketches.
The final word, though, must come from the Biblioteca Ambrosiana, the library in Milan, Italy, that houses the Codex Atlanticus, the largest collection of da Vinci's works.
Hohenstatt conducted the historical and artistic analysis of the drawing. Capasso, an anthropology professor at Gabriele d'Annunzio University in the medieval town of Chieti, Italy, handled the scientific and technical side of the work.
Capasso, who also serves as director of the university's museum, was credited in 2005 with reconstructing a da Vinci fingerprint from his manuscripts and the painting Lady with an Ermine. The fingerprint is one of the only biological traces of da Vinci, Capasso said.
Though the men cite several reasons for their conclusions, two elements are the most convincing, said Capasso.
First, the composition of the paper is almost identical to the paper used in three da Vinci sketches housed at the Uffizi Gallery in Florence, including The Landscape No. 8P, which da Vinci dated himself: August 5, 1473. All four works show evidence of lead salt treatment, which da Vinci commonly used to whiten his paper before applying inks and pigments, Capasso said.
The second element is where things get interesting: In volume 12, page 1033 of the Codex Atlanticus, there is a blank space with a glue silhouette that corresponds impressively with the paper on which the red-chalk sketch is drawn, Capasso said.
The glue on page 1033 even has a small imperfection that matches an imperfection in the glue on the back of the drawing.
Capasso said he has the chemical composition of the glue but cannot conduct a comparison with the codex until Biblioteca Ambrosiana permits an analysis.
Ambrosiana's vice prefect, Pier Francesco Fumagalli, declined to discuss the timing of the test. But in a letter to the sketch's owners, Fumagalli wrote that the library would permit a non-invasive analysis of the glue on page 1033.
The test will have to wait until at least 2012, he wrote, because the codex is in the process of being preserved.
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