Starting around 1853 and onward, he often spent summer months visiting Valmondois and Barbizon, where Corot, Daubigny, Millet, Rousseau, and others were painting, deepening his ties and friendships with the artist of the Barbizon School. By the mid to late 1850s Daumier had reached new levels of artistic maturity and increasingly wished to devote himself to painting. He was growing tired and weary of the grind and endless routine of producing new cartoons at a steady rate of two, three, sometimes as many as eight a week, yet he was dependent on the income. After 30 years of steadfast production, his caricatures were declining in popularity with the public, and in 1860 "Le Charivari" dropped him from their staff and ceases to publish his cartoons. While the next few years were a time of finical hardship and struggle, they were also years with free time to devote to painting, and a time of great productivity and artistic growth. Daumier exhibited regularly at the official Salon, although in this period of time it was only held once every two or three years. He suffered a serious illness in 1858.