14 colors were used to achieve this effect.
This picture is also known as "St. Veronica's Handkerchief" and is a copy of the celebrated painting by Gabriel Max, an Austrian, who was born in 1840. The original painting, valued at $25,000, is in a private collection in Prague, Austria. His best known work in America is "The Last Token" in the Metropolitan Museum of Art, New York.
It's never worked for me, but maybe it will for you. You might want to click on the picture to enlarge it before trying.