How computer science was used to reveal Gauguin’s printmaking techniques

A 1893 self-portrait of the French artist Paul Gauguin (1848-1903). Wikimedia Commons

Paul Gauguin’s art has always held special meaning for me. When I was six years old I spent a year on the small island of American Samoa. Faint memories of eating fresh guava plucked from trees, sliding down waterfalls and joining in Fia Fia – feasts where we would eat taro-root and chicken cooked in a pit – are triggered whenever I see Gauguin’s Tahitian imagery. So when I had a chance to lead a project on the technical analysis of the Gauguin’s prints, drawings and watercolors, I jumped at the opportunity.

Perhaps one of the best-known Post-Impressionist artists, Paul Gauguin was born in Paris in 1848 and died in the Marquesas Islands in 1903. His bold and vivid works first featured Bretons in various poses, but today he’s better-known for his “primitive” paintings of Tahitians surrounded by the flora and fauna of the South Pacific – what Gauguin saw as an exotic and pure land. Using a colorful palette and broad brushstrokes, he brought this region to life.

Paul Gauguin is best known for his brightly-colored paintings of Tahitians. Pictured is 1894’s ‘Day of the God (Mahana no Atua).’ The Art Institute of Chicago

But the artist also created a number of works on paper that included transfer drawings, which are also sometimes called monotypes – a fairly straightforward process that begins with a piece of paper being placed onto an inked surface. The artist then draws a picture on the back of the sheet using a pencil, and after the sheet is lifted from the inked surface, a final, unique image appears on the front. These transfer drawings are the focus of our study, which falls under an area of research often called technical art history.

Gauguin was never formally trained as a draftsman and printmaker, so he was unencumbered by traditional approaches to making graphic art, such as monotyping. As a result, Gauguin developed novel printmaking methods, employing highly experimental materials and fabrication techniques. For years, art historians and conservators puzzled over these prints: how did he form, layer and transfer images from one medium to another? More generally, how did he arrive at his artistic decisions?

Early last year, Harriet Stratis, senior research conservator at the Art Institute of Chicago, which houses one of the premier collections of Gauguin’s graphic works, wondered if my research group at the Center of Scientific Studies in the Arts at Northwestern University (NU-ACCESS) could answer these questions.

Faced with the challenge, we believed that we could unveil Gauguin’s printmaking methods by analyzing the surface topography of his prints. The minuscule details of the print surface could act as a “fingerprint” of Gauguin’s printmaking technique.

This level of detail can be difficult to discern with the naked eye, since such features are typically no higher or deeper than the width of a human hair (roughly 100 micrometers). Additionally, we needed to be able to examine and trace these micron-sized features over the entire print – not just a small, discrete area. However, visualization of microscopic features over wide areas is not a task suited to most methods of examination. We needed more sophisticated techniques, so we turned to a colleague in the Department of Computer Science and Electrical Engineering at Northwestern University, Professor Oliver Cossairt.

Cossairt specializes in an area of research known as computational imaging – essentially, a merging of computer science with photography. In particular, Cossairt’s research has focused on developing cameras capable of visualizing information beyond the limits of what the human eye can perceive. To better discern Gauguin’s printmaking methods, Cossairt helped implement photometric stereo, a simple computer vision technique first devised in 1980 as a way to digitally render real objects.

Photometric stereo allows researchers to view the topography of an object (in this case, an art print) by separating color from surface shape. In doing so, an object’s topography can be measured from the small changes in brightness that different lighting directions may cause.

For our study, we used Gauguin’s Nativity, a print the artist produced in 1902 using a transfer process that had perplexed conservators and art historians.

The left and right images depict the front and back, respectively, of Gauguin’s Nativity (1902). The Art Institute of Chicago

Nativity is a so-called “oil transfer drawing” on paper. In the image above, the front and back of the transfer drawing are shown. You can see the same general layout of the composition –- the back is a mirror image of the front. At first glance, the print looks like it was made by the simple monotyping method.

Upon closer inspection, however, it became clear that Gauguin’s printmaking process was more complex. Focusing on the section of a woman cradling a child, we noticed several regions contained lines where no ink or pigment had been applied. For decades, these features have been noted by art historians, who theorized that they’d been caused by so-called “blind incising” – indentations in the paper where ink simply wasn’t transferred.

Still, it had always been unclear how these blind incisions were introduced during the printmaking process – until now.

In the photometric stereo image of Nativity we clearly saw protrusions from the paper where ink was deposited – solid and indisputable evidence of the ink being transferred onto the print using monotyping. However, for the areas of blind incision we expected to see an indentation in the paper corresponding to what we thought was Gauguin’s techqniue: drawing on a stack of papers and transferring impressions of his drawing to sheets below (think of how writing on a pad of paper can transfer impressions to the underlying sheets). However, we observed no topography at all in these areas. Indeed, the “blind incisions” on this print could not have been made by impressing the paper.

Subtle topographical features reveal printmaking techniques (click to zoom). Visible in the top left panel and the top right 3D rendering are line protrusions from the monotype printing. In the bottom left image, one area of ‘blind incision’ is marked by the arrow. In the bottom right panel, the corresponding area is pictured after photometric stereo. Author provided

Perplexed by this paradox, we mapped out all of the paper’s blind incisions, and a new idea emerged: we were looking at impressions made from the inked surface, rather than elements contained in the paper. We developed a new hypothesis that Gauguin used a hard and flat material (such as a glass slab), covered it in ink, and then created multiple monotypes of different images from this inked matrix. In doing so, he left behind a palimpsest of un-inked areas from earlier drawings that would be transferred onto a piece of paper as blank lines with no surface topography. We confirmed this suspicion by replicating this process making prints with ‘blind incisions’ that matched what we found on Nativity, even at microscopic magnification.

Reproductions of inked glass supports, from which Gauguin likely pulled several prints. Author provided

Using photometric stereo – a non-invasive and cost-effective technique – on additional works of Gauguin’s will enable us to firmly establish how the artist approached printmaking.

And beyond Gauguin, the study shows how collaboration between science and the humanities can create exciting avenues of discovery.