Researchers have found how famed French artist Paul Gauguin formed, layered and re-used imagery to make 19 unique graphic works.
Gauguin is well known for his colourful paintings of Tahitian life - including the one that sold recently for nearly USD 300 million - but he also was a highly experimental printmaker, researchers said.
Little is known, however, about the techniques and materials Gauguin used to create his unusual and complex graphic works.
Now a team of scientists and art conservators from Northwestern University and the Art Institute of Chicago has used a simple light bulb, an SLR camera and computational power to uncover new details of Gauguin's printmaking process - how he formed, layered and re-used imagery to make 19 unique graphic works in the Art Institute's collection.
The new results establish Gauguin's use of materials and process in a chronological order, solving the puzzle of how "Nativity" was made.
Gauguin created the print using a layering of images created on paper by drawings, transfer of images and two different inks.
The "Nativity" findings overturn an earlier theory as to how Gauguin might have produced the print.
The printmaking process the research team had identified produced a print very similar to Gauguin's original.
"To measure the 3-D surface of the prints, we used some very accessible techniques that can be used by art conservators and historians around the world to analyse artworks," said computer scientist Oliver S Cossairt, who developed the software to analyse the imaging data.
Cossairt and his colleagues used multiple wavelengths of light shining from different directions onto the prints to investigate the surface of the paper and reevaluate how Gauguin created his works.
The photometric stereo technique allowed the researchers to mathematically separate colour from surface shape, providing a much clearer view of the paper's topography.
For the study of an artwork, the piece was fixed in place, as was an SLR camera. A light bulb was moved to 20 different locations and a photo taken of the artwork for each light bulb position.
The digital data for each pixel of each image then was run through Cossairt's software. Researchers measured only the response of an artwork's surface to changing lighting.
The surface structure of "Nativity" showed solid evidence that the white lines, in which there is an absence of ink, are on a flat surface.
This indicates those lines were not produced using a relief process but rather a transfer process, where Gauguin drew on an inked surface, removing ink, and those empty lines were transferred to his print.
The findings also show Gauguin would have placed his paper on an inked surface and then drawn on the back of the paper, causing ink to be transferred to the paper where pressure from the artist's pencil was applied.
