From the Telegraph:
For as long as man has painted, he (and it usually is a he) has painted his lovers. Look at any of the great works of Western art and, chances are, you will find a mistress, girlfriend, wife or prostitute centre stage.
They may not announce themselves as such, going under the discreet title of Woman Sewing, Girls Bathing or simply Repose. But they’re there all right, these soul mates and play mates, lighting up the canvas with a particular kind of intimacy.
As all these examples suggest, a cloud of suspicion hung over male artists and their choice of female subjects. Painting a wife or sister might seem the obvious way of sidestepping adverse comment, but the problem was that at that time the act of putting a respectable woman on view tarnished her reputation. So there was no choice but to go looking for women who had nothing to lose and perhaps something to gain – the affection of an interesting man, the warmth of the studio, a meal – by becoming public property.