This wide-eyed young boy looks up in wonder at a large bubble he has just blown. The bowl in his lap is full of soapsuds, and the pipe in his hand is for blowing bubbles. This is one of the best-known works by the Victorian artist, John Everett Millais. As a young artist, Millais was one of the Pre-Raphaelite painters, but he painted this work in his fifties, when the bright colours and precise details of his earlier work had given way to darker tones and looser brushwork. The young boy was his grandson, William Milbourne James, who was about four years of age at the time. Millais called it 'A Child's World', referring to the utter engrossment of children. But there's a moral here too, which derives from 17th-century Dutch paintings. The bubbles represent the brevity of human life: just as bubbles inevitably burst, thus youth and innocence also pass. But this image has endured, because the year after it was painted it was bought by the chairman of Pear's Soap and reproduced as a poster. It was probably the first work of art ever to be used in advertising. The message was clear: wash with Pear's and you'll be as clean and pure as this child.