In 1879, Blum joined his friend William Merritt Chase in Venice. During his two-year stay he was neighbor to James McNeill Whistler, who instructed Blum in the principles of Japanese design and also encouraged his use of pastels, a medium that Whistler was then using with extraordinary results. Blum later observed, "I know [Whistler] well. He is a very nice man," an opinion not widely shared at the time.

Pastel indeed was a medium well suited to the suggestiveness and rapid notation of Blum's technique. Blum and his good friend Chase became the preeminent exponents of pastel technique in America, and together they founded the Society of Painters in Pastels, an organization that was instrumental in hastening acceptance of the impressionist aesthetic on these shores. Oscar Wilde, a great admirer of Blum's work, told him, "your exquisite pastels give me the sensation of eating yellow satin."

While living in Venice, Blum sought out subject matter in the less frequented quarters of the city. Venetian Lace Makers (1887), his first important canvas, painted in Burano, won him several medals and an associate membership in the National Academy of Design. With loose brushwork, a dark palette, and dramatic contrasts, the canvas depicts two young women deeply concentrating on their demanding task.

The vertical format of Canal in Venice emphasizes the narrowness of the canal and the height of the adjacent buildings. The watery foreground with its vertical reflections and the contrasting distribution of tones in adjoining buildings lead the eye toward the bridge and the central structure. The dominant mass of the building on the right is offset by the eye-catching patch of white in the upper left section. The whole is enlivened by contrasting tones of light and shade and bravura brushwork.

Years later, a professional commission at last took him to Japan, "the most glorious experience I have ever had," he reported. Not long after, at the age of forty-six, Blum died of pneumonia, his promising career ended.