The American artist Mary Cassatt established herself in Paris’s art scene with paintings like Little Girl in a Blue Armchair. She regularly exhibited at the annual Paris Salon beginning in 1868 and was the only American (and one of only four women) in the independent impressionists group. Today, most know Cassatt for her works on canvas.

But Cassatt was also one of the most innovative printmakers of her generation. The messy, time-consuming work of printmaking requires special equipment and skills, which might have seemed daunting to certain 19th-century painters. Not Mary Cassatt. From the creation of her first prints around 1879 in the company of fellow impressionist Edgar Degas, her creativity was sparked. As Cassatt embraced printmaking and mastered its technical challenges, it pushed her in new directions as an artist.

Cassatt was a quick learner. About a year after Degas introduced her to the process, she collaborated with him, Camille Pissarro, Félix Bracquemond, and Gustave Caillebotte on a journal of prints, Le Jour et la Nuit (Day and Night). While the project was never completed (due to Degas’s apparent inability to follow through on his ambitious ideas), the experience gave Cassatt a solid foundation in printmaking. Working closely with the other artists, she learned the techniques of softground etching, drypoint, and aquatint.

Cassatt threw herself into to the project. For her contribution to the journal she created an image of a woman in an opera box, a theme she had explored in pastels and paintings.

Though Le Jour et la Nuit was never completed, Cassatt did not make her contribution in vain—she, Degas, and Pissarro exhibited prints, including some of the trial-and-error proofs from the unrealized project in the fifth impressionist exhibition in 1880. Cassatt continued to develop her printmaking prowess over the course of the next three decades.

In the spring of 1890, a major exhibition of Japanese woodcuts swept the Parisian art world. Cassatt found it revelatory, writing to fellow artist Berthe Morisot, “I can’t think of anything else but color on copper.” Already a collector of Japanese prints, Cassatt became consumed with adapting their vibrant hues, flat forms, and strong lines into prints of her own work. This spark of inspiration would lead her to create what is now known as her Set of 10.

The ambitious and technically complex group of color prints required Cassatt to stretch her already strong skills. Color printing was a relatively new beast to her. Later, she reflected, “I was entirely ignorant of the method when I began.” She engaged printer Modeste Leroy to realize her vision and help produce the works together in her studio. (Each of the images was printed from two or three plates, inked with different colors, in alignment and sequence.) Her studio became a laboratory as she experimented with combining different techniques, adjusting tones, and revising compositions.

In less than a year, Cassatt created and finalized 10 images, putting in long hours with Leroy to print 25 copies of each one. The group shows women’s private and public lives. Prints like The Coiffure nod to Japanese prints she admired. Others including Mother’s Kiss and Maternal Caress depict the embrace of a mother and child, a theme she was simultaneously exploring in other mediums.

The range of color, tone, and texture in the Set of 10 is astounding. Works like The Letter are rich in overlapping details, printed in a distinctive style that was entirely Cassatt’s own. So how did she make these radical prints?

Although Cassatt’s prints often revisited the subjects of her paintings and drawings, In the Omnibus depicts a subject she did not explore in any other medium. Our unique group of six works for In the Omnibus, part of her Set of 10, offers a glimpse of Cassatt’s mind at work. Through them we can track her process from a preparatory drawing to the final color print.

Cassatt started with a chalk-and-graphite drawing, which she wrapped around a copper plate coated with softground. You can see the tabs where the drawing was wrapped along the upper left and lower right edges.

Then, she traced the outline she wanted to transfer to the plate—the reverse of the drawing (seen below) shows these softground lines. Notice the details she chose to transfer: the two seated women and the baby, along with the horizontal and vertical lines of the omnibus windows. If you look closely at the drawing above, you can see traces of a seated man with a top hat and cane, and a standing woman in profile. Cassatt toyed with the idea of including these passengers, but ultimately decided to simplify the composition and focus on the group of three.

For Cassatt, transferring her preparatory drawing to her first copper plate was only the beginning. The iterative nature of printmaking enabled her to continue revising In the Omnibus, which she ultimately printed from three plates.

The first of the four below proofs show how Cassatt used the drypoint technique. Using a sharp tool, she scratched directly into her plate (and over the guide of the softground etching lines) to define the figures and the omnibus interior. She then used aquatint to add color to the seats, women’s dresses and hats, the ball in the baby’s left hand, and the distant bridge and riverbanks.

Cassatt explored different colors, testing a palette of peach, coral, and teal.  She tried using flesh tones to print the faces of all three figures, but in the end left the white of the paper with discrete touches of color on their lips instead.

Fully satisfied, Cassatt made her final print. She signed the lower right of impressions with both her and Leroy's names to acknowledge his contributions.

Cassatt’s grand experiment was a grand success. After an exhibition of the Set of 10 by her dealer Durand-Ruel in Paris in 1891, she received acclaim from both critics and artists. Fellow impressionist and color printmaker Camille Pissarro complimented her ability to tame the unwieldy printmaking process and create prints “as beautiful as Japanese work.”

In subsequent years Cassatt regularly exhibited her prints; an 1893 exhibition, the artist's first retrospective, included 67 prints alone. In the end she made more than 200. Reflecting in 1898 on her remarkable body of work, a critic stated that it would be unwise for any other artists to “dispute the field with her.”