This picture is full of intriguing details. When the work was conserved in 2008, x-rays revealed that, in between the clock and the hourglass (detail pictured), a woman could be seen at the side of the picture, looking in towards the centre of the composition. Before conservation, she was invisible to the naked eye, but now we can see the faint pale blur of her face to the upper left of the clock.
There are various theories as to why she was painted out - was she Robert Paston's elder daughter, who scandalised her family by eloping with an unsuitable man? Or was she Paston's wife, Rebecca? No-one really knows.
We do know that in contemporary iconography the clock, the hourglass and the guttering candle in that part of the picture are all references to death. It it believed that the Pastons' younger daughter, Mary, shown here in the centre, died while the picture was being painted. Perhaps the artist changed the emphasis of the painting accordingly, removing the third figure and adding instead unmistakable references to the passing of time and the frailty of human life.