This is a silkscreen print. The original image was grainy photograph of an electric chair. The photo was featured in newspapers.
See Little Electric Chair on Christie's Auction House
"Ironically, at the time the work was created in 1964, the electric chair had been recently outlawed in the state of New York, having become a subject of controversy that was widely reported in the news. Its last two executions took place in the Sing Sing State Penitentiary on March 21 and August 15 of 1963, in the executions of Frederick Charles Wood and Eddie Lee Mays.
Rendered in black silkscreen ink upon a background of cool, blue acrylic, Warhol’s Little Electric Chair is a somber reminder of execution process."
Vocab: Silkscreen, Pop Art, 20th Century