Like many classically trained painters, Eugène Delacroix (1798–1863) learned to use pastels primarily to make sketches and studies when preparing to paint in oils. He trained under Pierre-Narcisse Guérin, largely in the Neoclassical style advanced by Jacques-Louis David, and was soon inspired by Théodore Géricault’s more Romantic Raft of the Medusa (1818-19) to early success at the Salon in 1822.
His use of pastels to work up major oil paintings is illustrated by two of the surviving studies he made for The Death of Sardanapalus (1827-28).

Here he has been working on the figures of a courtesan who has flung herself on the divan, at the feet of Sardanapalus, and a slave struggling with a horse.

This is a study for a courtesan in the foreground, who is just about to have her throat cut.

This is his first full-size finished oil painting, showing how those studies informed his completed work.
Some of his later pastel paintings followed rather than preceded finished works, as he used them as quick copies to give to his friends.

For example, his pastel version of Christ on the Cross was painted in 1847-50, and is derived from his oil original completed in 1846, now in the Walters in Baltimore. That finished work had at least one preparatory pastel study, in which Delacroix evolved his painting from Rubens’ Coup de Lance or Christ on the Cross of 1619-20.
Lee Johnson has proposed that Delacroix painted this derivative for Haro, who supplied the artist with his materials, when the latter came to admire his oil original at the Salon in 1847.
Delacroix is one of the few French artists of that time who used ‘skying’ studies to inform his finished paintings, as John Constable had done earlier in the century. Several of Delacroix’s pastels from around 1850 appear to have been made in front of glorious sunsets out in the country, probably near his cottage at Champrosay outside Paris.

This Study of the Sky at Sunset from 1849 is now in the Louvre.

The Met in New York has this slightly later Sunset from about 1850. Again, Delacroix had an ulterior motive, as can be seen in his painted ceiling in the Louvre’s Galerie d’Apollon, which he made between 1848-50.

Delacroix also experimented with mixed media almost a century before that became popular. He painted this detailed Bouquet of Flowers in 1849-50 using the combination of watercolour, gouache and pastel on paper. Others before and since brushed their pastels, and several wetted them, but this combination was well in advance of its time.

When he was in Paris, one of Delacroix’s favourite activities was to visit the zoo at the city’s Jardin des Plantes and sketch the big cats there. He sometimes used pastels for this purpose, and this painting of a Tiger Preparing to Spring from about 1850 demonstrates his mastery of the medium.

Saint Sebastian Tended by the Holy Women, painted in pastels between 1852-54, is thought to be a simplified copy of his large finished oil painting of the same subject completed in 1836. Delacroix wrote on the back of this to record that he gave it to Jenny Leguillou on 25 March 1855, perhaps as a devotional for her. She lived from 1801-1869, and he had painted her portrait in oils in about 1840. She had been the artist’s housekeeper and friend since entering his service in 1835.

Delacroix’s last known pastel painting is one of his finest. The Education of Achilles, painted in about 1862, shows the ‘wisest and justest of all the centaurs’ Chiron teaching Achilles to hunt. The artist gave this to his longstanding friend Aurore Dudevant, better known under her pen name of George Sand.
This wasn’t his first painting of this scene; back in 1838-47 he had included it the corner of a ceiling in the library of the Palais Bourbon, and there’s a surviving graphite sketch he made for that dated to about 1844. He seems to have been painting an easel version in his studio when Sand/Dudevant visited him in about 1862. She took a liking to the painting, which had already been promised to someone else, so he made this replica in pastels as a gift for her. Whether he ever completed the oil version isn’t clear, and I haven’t been able to trace it, but the following year Delacroix died, with Jenny Leguillou beside him.
Delacroix left Jenny Leguillou sufficient money to live the remainder of her life in comfort. The following year the contents of his studio were sold, including 853 oil paintings and over 1500 pastels, the great majority of which have since disappeared.